General Chemistry Exam #1
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This is the General Chemistry Exam #1. Please read the following tips before beginning:
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You will have 30 minutes to answer 30 questions.
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Question 1 of 30
1. Question
Which of the following acids is strongest? The acid is followed by its \( pK_a \) value
Correct
The \( pK_a \) is a measure of the strength of acids and the higher value means the weaker acid. According to the value of \( pK_a \), \( HClO_3 \) is the Strong acid and completely dissociate in aq solution.
Incorrect
The \( pK_a \) is a measure of the strength of acids and the higher value means the weaker acid. According to the value of \( pK_a \), \( HClO_3 \) is the Strong acid and completely dissociate in aq solution.
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Question 2 of 30
2. Question
Which diagram shows the titration of \( H_3PO_4 \)?
Correct
The acid and base equivalence point is a point at which the moles of the titrant and analyte are equal. The first equivalence point of H3PO4 corresponds to the conversion of H3PO4 to H2PO4– Ka1and the second equivalence point corresponds to the conversion of H2PO4– to HPO4 2- Ka2and the third equivalence point corresponds to the conversion HPO42- to PO43-. Ka3
Incorrect
The acid and base equivalence point is a point at which the moles of the titrant and analyte are equal. The first equivalence point of H3PO4 corresponds to the conversion of H3PO4 to H2PO4– Ka1and the second equivalence point corresponds to the conversion of H2PO4– to HPO4 2- Ka2and the third equivalence point corresponds to the conversion HPO42- to PO43-. Ka3
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Question 3 of 30
3. Question
Which of the following acids will have the strongest conjugate base?
Correct
The acid with the strongest conjugate base will be the weakest acid of the group. According to the value of pKa, HCN is the only weak acid listed among the choices.
Incorrect
The acid with the strongest conjugate base will be the weakest acid of the group. According to the value of pKa, HCN is the only weak acid listed among the choices.
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Question 4 of 30
4. Question
Which of the following compounds is polar?
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Question 5 of 30
5. Question
Which of the following is the correct bond angle found in BH3?
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Question 6 of 30
6. Question
Correct
In chemistry, an ionic compound is a chemical compound composed of ions held together by electrostatic forces termed ionic bonding. Ionic Solids are solids composed of oppositely charged ions. They consist of positively charged cations and negatively charged anions .When Ionic Solids are dissolved in water the cations and the anions separate, they become free to move about in the water allowing the solution to conduct electrical current.
For cesium chloride, you could draw a simple diagram showing the arrangement of the chloride ions around each cesium ion.
The above mentioned content is applied about MgBr2 too.Incorrect
In chemistry, an ionic compound is a chemical compound composed of ions held together by electrostatic forces termed ionic bonding. Ionic Solids are solids composed of oppositely charged ions. They consist of positively charged cations and negatively charged anions .When Ionic Solids are dissolved in water the cations and the anions separate, they become free to move about in the water allowing the solution to conduct electrical current.
For cesium chloride, you could draw a simple diagram showing the arrangement of the chloride ions around each cesium ion.
The above mentioned content is applied about MgBr2 too. -
Question 7 of 30
7. Question
A mixture of O2, SO2, and SO3 contains 0.077 M SO2, 0.077 M SO3 and 0.087M O2 in a 1 L container. What is the equilibrium constant of the following reaction?
2SO2(g)+O2(g)⇌2SO3(g)
Correct
The equilibrium constant is calculated by the equation below
Kc = [SO3]2 / [SO2]2 [O2]
Kc= [0.077]2/ [0.077]2 [0.087] Kc= 1.15
Incorrect
The equilibrium constant is calculated by the equation below
Kc = [SO3]2 / [SO2]2 [O2]
Kc= [0.077]2/ [0.077]2 [0.087] Kc= 1.15
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Question 8 of 30
8. Question
If the Ksp of Fe(OH)3 is \( 4\times 10^{-38} \), calculate the molar solubility of Fe(OH)3 in a pH = 5.0 buffer solution.
Correct
we must first calculate the [OH¯]. To do this, we will use the pH and acid base concepts. Then, we will use the Ksp expression to calculate the Ksp
Using pOH = -log 10 ([OH–]) pH + pOH = 14.0
pOH = (14.0 – 5.0) = 9.0 and [OH–] = 1× 10-9 M
The solubility equilibrium and product are
Fe(OH)3(s)⇌ Fe3+(aq) + 3OH–(aq) Ksp = [Fe3+][OH–]3
\( [Fe^{3+}] =\frac{[Ksp]}{[OH-]3}= 4 \times 10^{-38}/( 1\times 10^{-9})^3 = 4×10^{-11} M \)
Incorrect
we must first calculate the [OH¯]. To do this, we will use the pH and acid base concepts. Then, we will use the Ksp expression to calculate the Ksp
Using pOH = -log 10 ([OH–]) pH + pOH = 14.0
pOH = (14.0 – 5.0) = 9.0 and [OH–] = 1× 10-9 M
The solubility equilibrium and product are
Fe(OH)3(s)⇌ Fe3+(aq) + 3OH–(aq) Ksp = [Fe3+][OH–]3
\( [Fe^{3+}] =\frac{[Ksp]}{[OH-]3}= 4 \times 10^{-38}/( 1\times 10^{-9})^3 = 4×10^{-11} M \)
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Question 9 of 30
9. Question
Regarding the following reaction :
\( N_2 O_5 (g)→4 NO_2 (g)+ O_2 (g) \)
During 80 seconds, 9.2 g of \( NO_2 \) gas is produced. What is the average rate of \( NO_2 \) in terms of mole/min?
Correct
\[ R_{NO2}=\frac{(9.2/46 mol)}{(80/60 min)}=0.15mole.min^{(-1)} \]
Incorrect
\[ R_{NO2}=\frac{(9.2/46 mol)}{(80/60 min)}=0.15mole.min^{(-1)} \]
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Question 10 of 30
10. Question
What is the overall order of a particular reaction that has a rate constant of 1.3 × 10-4M-1 S-1?
Correct
The unit for K is M-1 S-1, so the rate of the reaction is calculated according to the equation below: Rate= K [A]2. The overall reaction is a second-order reaction.
Incorrect
The unit for K is M-1 S-1, so the rate of the reaction is calculated according to the equation below: Rate= K [A]2. The overall reaction is a second-order reaction.
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Question 11 of 30
11. Question
If a student intends to prepare 50ml of a 0.100 M solution of HCl from 37% hydrochloric acid, how many liters of HCL does the student need?
Correct
\[ 50 ml \times \frac{0.1mol}{1lit} \times \frac{1lit}{1000ml} \times \frac{100gr}{37 gr} \times \frac{37 gr}{1 mol} \times \frac{1ml}{1.18gr}= 0.42 ml \]
Incorrect
\[ 50 ml \times \frac{0.1mol}{1lit} \times \frac{1lit}{1000ml} \times \frac{100gr}{37 gr} \times \frac{37 gr}{1 mol} \times \frac{1ml}{1.18gr}= 0.42 ml \]
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Question 12 of 30
12. Question
Which of the following is NOT correct about solutions?
Correct
A solution is a special type of homogeneous mixture composed of two or more substances. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent. The mixing process of a solution happens at a scale where the effects of chemical polarity are involved, resulting in interactions that are specific to solvation. The solution assumes the phase of the solvent when the solvent is the larger fraction of the mixture, as is commonly the case. The concentration of a solute in a solution is the mass of that solute expressed as a percentage of the mass of the whole solution. The term aqueous solution is when one of the solvents is water.
Incorrect
A solution is a special type of homogeneous mixture composed of two or more substances. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent. The mixing process of a solution happens at a scale where the effects of chemical polarity are involved, resulting in interactions that are specific to solvation. The solution assumes the phase of the solvent when the solvent is the larger fraction of the mixture, as is commonly the case. The concentration of a solute in a solution is the mass of that solute expressed as a percentage of the mass of the whole solution. The term aqueous solution is when one of the solvents is water.
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Question 13 of 30
13. Question
What is the concentration of nitrate (NO3-) in each of the following aqueous solutions respectively?
1) 0.25 M KNO3
2) 0.10 M Al (NO3)3
3) 0.20 M Ca(NO3)2
Correct
\[ NO_3^{-1}=\frac{0.25 \text{ mol } KNO3}{L} \times \frac{1 { \text{ mol }} NO3^{-1}}{\text{mol }KNO3}=0.25 \text{ M} \]
\[ NO_3^{-1}=\frac{0.10 \text{ mol Al} (NO3)3}{L} \times \frac{3 { \text{ mol }} NO3^{-1}}{\text{mol Al }(NO3)3}=0.30 \text{ M} \]
\[ NO_3^{-1}=\frac{0.20 \text{ mol Ca} (NO3)2}{L} \times \frac{2 { \text{ mol }} NO3^{-1}}{\text{mol Ca }(NO3)2}=0.40 \text{ M} \]
Incorrect
\[ NO_3^{-1}=\frac{0.25 \text{ mol } KNO3}{L} \times \frac{1 { \text{ mol }} NO3^{-1}}{\text{mol }KNO3}=0.25 \text{ M} \]
\[ NO_3^{-1}=\frac{0.10 \text{ mol Al} (NO3)3}{L} \times \frac{3 { \text{ mol }} NO3^{-1}}{\text{mol Al }(NO3)3}=0.30 \text{ M} \]
\[ NO_3^{-1}=\frac{0.20 \text{ mol Ca} (NO3)2}{L} \times \frac{2 { \text{ mol }} NO3^{-1}}{\text{mol Ca }(NO3)2}=0.40 \text{ M} \]
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Question 14 of 30
14. Question
If 0.50 mol of an ideal gas occupies a volume of 2.50 l at 25oC, calculate the pressure of the gas.
Correct
The pressure of an ideal gas can be calculated by the equation below
PV= nRT
At first, we have to convert 25⁰C to kelvin T= 25.0 + 273= 298 K
V= 2.50 l , n= 0.50 mol , \( R= 0.0821 \frac{l\text { } atm}{mol\text { } K} \)
\[ P=\frac{n RT}{V}=\frac{0.50mol \times 0.0821 \frac{l\text { } atm}{mol\text { } K} \times 298K}{2.50l}=4.89 \]
Rounding off 4.89 to 4.9 atm.
Incorrect
The pressure of an ideal gas can be calculated by the equation below
PV= nRT
At first, we have to convert 25⁰C to kelvin T= 25.0 + 273= 298 K
V= 2.50 l , n= 0.50 mol , \( R= 0.0821 \frac{l\text { } atm}{mol\text { } K} \)
\[ P=\frac{n RT}{V}=\frac{0.50mol \times 0.0821 \frac{l\text { } atm}{mol\text { } K} \times 298K}{2.50l}=4.89 \]
Rounding off 4.89 to 4.9 atm.
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Question 15 of 30
15. Question
What will be the volume of an ideal gas at a constant temperature when the pressure of the gas is increased from 0.8 atm to 1.6 atm and its initial volume is 1.5 L?
Correct
The pressure of a gas is inversely proportional to its volume when the temperature is constant. If the temperature of a system remains the same over a given time. It is used in Boyle’s law
P1V1= P2V2
P1 and V1=initial pressure and volume
P2 and V2= final pressure and volume
0.8(atm) × 1.5 (l) = 1.6 (atm) × X (l) X= 0.75 l
Incorrect
The pressure of a gas is inversely proportional to its volume when the temperature is constant. If the temperature of a system remains the same over a given time. It is used in Boyle’s law
P1V1= P2V2
P1 and V1=initial pressure and volume
P2 and V2= final pressure and volume
0.8(atm) × 1.5 (l) = 1.6 (atm) × X (l) X= 0.75 l
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Question 16 of 30
16. Question
Which of the following elements will have the greatest reactivity with chlorine?
Correct
Metals have fewer electrons in their outer shell compared to non-metals and hence in reactions, they give away their outermost electrons to the non-metals, as it is easier to get rid of few electrons than many. As we work our way down group 2, each successive element has an increasing number of shells and hence an increased atomic radius, so the outermost electrons experience less attraction to the nucleus and can be transferred to the non-metal element more easily.
Incorrect
Metals have fewer electrons in their outer shell compared to non-metals and hence in reactions, they give away their outermost electrons to the non-metals, as it is easier to get rid of few electrons than many. As we work our way down group 2, each successive element has an increasing number of shells and hence an increased atomic radius, so the outermost electrons experience less attraction to the nucleus and can be transferred to the non-metal element more easily.
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Question 17 of 30
17. Question
Which of the following descriptions is incorrect for the chemical tool mentioned for it?
Description Tool 1
Measure the volume of a liquid
Graduated cylinder
2
Guide liquid or powder into small opening
Funnel
3
Use for mixing or heating chemicals Test tube
4
Measure mass accurately
Flask
5
Transport a measured volume of liquid
pipette
Correct
Flask is commonly used for containing liquid and performing mixing, heating, cooling, precipitation, condensation, and other processes.
Incorrect
Flask is commonly used for containing liquid and performing mixing, heating, cooling, precipitation, condensation, and other processes.
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Question 18 of 30
18. Question
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Question 19 of 30
19. Question
Which of the following is the strongest of the inter-molecular forces?
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Question 20 of 30
20. Question
In which salt [that is crystallized in the NaCl system] the difference of measured and experimental values of lattice energy is higher than the others?
Correct
By decreasing the covalent property of ionic composition, the experimental value of lattice energy will be more. It has more difference with its measured value because the covalent property of CsF is less than the others. Therefore we can expect that the lattice energy of CsF is higher than the others.
Incorrect
By decreasing the covalent property of ionic composition, the experimental value of lattice energy will be more. It has more difference with its measured value because the covalent property of CsF is less than the others. Therefore we can expect that the lattice energy of CsF is higher than the others.
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Question 21 of 30
21. Question
What is the missing particle in the following nuclear reaction?
23993Np → 23994Pu + X
Correct
All nuclear reactions must be balanced in mass number and atomic number. To balance the equation above for mass, charge, and mass number, the second nucleus on the right side must have atomic number 0 and mass number -1; it is therefore also 0-1e.
Incorrect
All nuclear reactions must be balanced in mass number and atomic number. To balance the equation above for mass, charge, and mass number, the second nucleus on the right side must have atomic number 0 and mass number -1; it is therefore also 0-1e.
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Question 22 of 30
22. Question
Which of the following metals is the strongest reducing agent?
Correct
Reduction potential (Eh) is the measurement of the tendency of an environment to oxidize substrates. Strong reducing agents can be said to have high electron-transfer potential. Therefore Li is the strongest reducing agent.
Incorrect
Reduction potential (Eh) is the measurement of the tendency of an environment to oxidize substrates. Strong reducing agents can be said to have high electron-transfer potential. Therefore Li is the strongest reducing agent.
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Question 23 of 30
23. Question
Which of the following statements is INCORRECT regarding electrolytic cells?
Correct
An electrolytic cell is an electrochemical cell that drives a non-spontaneous redox reaction through the application of electrical energy. They are often used to decompose chemical compounds.
Galvanic cells compared to electrolytic cells:
In an electrolytic cell, the current is passed through the cell by an external voltage, causing an otherwise nonspontaneous chemical reaction to proceed. In a galvanic cell, the progress of a spontaneous chemical reaction causes an electric current to flow. An equilibrium electrochemical cell is at the state between an electrolytic cell and a galvanic cell. The tendency of a spontaneous reaction to push a current through the external circuit is exactly balanced by an external voltage that is called a counter electromotive force or counter e.m.f. so that no current flows. If this counter voltage is increased the cell becomes an electrolytic cell and if it is decreased the cell becomes a galvanic cell.Incorrect
An electrolytic cell is an electrochemical cell that drives a non-spontaneous redox reaction through the application of electrical energy. They are often used to decompose chemical compounds.
Galvanic cells compared to electrolytic cells:
In an electrolytic cell, the current is passed through the cell by an external voltage, causing an otherwise nonspontaneous chemical reaction to proceed. In a galvanic cell, the progress of a spontaneous chemical reaction causes an electric current to flow. An equilibrium electrochemical cell is at the state between an electrolytic cell and a galvanic cell. The tendency of a spontaneous reaction to push a current through the external circuit is exactly balanced by an external voltage that is called a counter electromotive force or counter e.m.f. so that no current flows. If this counter voltage is increased the cell becomes an electrolytic cell and if it is decreased the cell becomes a galvanic cell. -
Question 24 of 30
24. Question
According to the periodic law, when elements are arranged in order of increasing _____________, there is a periodic repetition of their _____________ properties.
Correct
When Mendeleev’s table is ordered by the atomic number, the discrepancies within this table disappear. Tellurium has an atomic number of 52, while iodine has an atomic number of 53. So even though tellurium does indeed have a greater atomic mass than iodine, it is properly placed before iodine in the periodic table. Mendeleev and Moseley are credited with being most responsible for the modern periodic law: when elements are arranged in order of increasing atomic number, there is a periodic repetition of their chemical and physical properties. The result is the periodic table as we know it today. Each new horizontal row of the periodic table corresponds to the beginning of a new period because a new principal energy level is being filled with electrons. Elements with similar chemical properties appear at regular intervals, within the vertical columns called groups.
Incorrect
When Mendeleev’s table is ordered by the atomic number, the discrepancies within this table disappear. Tellurium has an atomic number of 52, while iodine has an atomic number of 53. So even though tellurium does indeed have a greater atomic mass than iodine, it is properly placed before iodine in the periodic table. Mendeleev and Moseley are credited with being most responsible for the modern periodic law: when elements are arranged in order of increasing atomic number, there is a periodic repetition of their chemical and physical properties. The result is the periodic table as we know it today. Each new horizontal row of the periodic table corresponds to the beginning of a new period because a new principal energy level is being filled with electrons. Elements with similar chemical properties appear at regular intervals, within the vertical columns called groups.
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Question 25 of 30
25. Question
Which of the following is correct about electronegativity?
Correct
Electronegativities generally increase from left to right across a period. This is due to an increase in nuclear charge. Alkali metals have the lowest electronegativities, while halogens have the highest. Because most noble gases do not form compounds, they do not have electronegativities. Note that there is little variation among the transition metals. Electronegativities generally decrease from top to bottom within a group due to the larger atomic size.
Incorrect
Electronegativities generally increase from left to right across a period. This is due to an increase in nuclear charge. Alkali metals have the lowest electronegativities, while halogens have the highest. Because most noble gases do not form compounds, they do not have electronegativities. Note that there is little variation among the transition metals. Electronegativities generally decrease from top to bottom within a group due to the larger atomic size.
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Question 26 of 30
26. Question
An unknown compound contains 2.82g Na, 4.35g Cl and 7.83g O. What is the empirical formula of the compound?
Correct
\[ \text{mol }Na=\frac{2.82 \text{ g }Na}{23 \text{ g }/mol}=0.1226 \]
\[ \text{mol }Cl=\frac{4.35 \text{ g }Cl}{35.45 \text{ g }/mol}=0.1227 \]
\[ \text{mol }O=\frac{7.83 \text{ g }O}{16 \text{ g }/mol}=0.4894 \]
We should divide the numbers above by the lowest number of moles.
\[ \text{ for } Na=\frac{0.1226}{0.1226}=1 \\ \text{ for } Cl=\frac{0.1227}{0.1226} \approx 1 \\ \text{ for } O=\frac{0.4894}{0.1226}=4 \]
The empirical formula is NaClO4
Incorrect
\[ \text{mol }Na=\frac{2.82 \text{ g }Na}{23 \text{ g }/mol}=0.1226 \]
\[ \text{mol }Cl=\frac{4.35 \text{ g }Cl}{35.45 \text{ g }/mol}=0.1227 \]
\[ \text{mol }O=\frac{7.83 \text{ g }O}{16 \text{ g }/mol}=0.4894 \]
We should divide the numbers above by the lowest number of moles.
\[ \text{ for } Na=\frac{0.1226}{0.1226}=1 \\ \text{ for } Cl=\frac{0.1227}{0.1226} \approx 1 \\ \text{ for } O=\frac{0.4894}{0.1226}=4 \]
The empirical formula is NaClO4
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Question 27 of 30
27. Question
What is the atomic mass of element X when 3.625 g of element X combined with 1.476 g of oxygen to form X2O3?
Correct
\[ \text{ mass of }X =\text{ mass of oxygen } \times \frac{1}{\text{ molar mass of O }} \times \frac{\text{ 2 mol X} }{\text{ 3 mol O}} \times \text{molar mass of X} \]
We should substitute 3.625 g for mass of X and 1.476 g for mass of O
\[ 3.625 g = 1.476 g × \frac{1}{16 g/mol} × 2/3 × \text{ molar mass of X } \\ \text{ Molar mass } X \approx 59 \]
Incorrect
\[ \text{ mass of }X =\text{ mass of oxygen } \times \frac{1}{\text{ molar mass of O }} \times \frac{\text{ 2 mol X} }{\text{ 3 mol O}} \times \text{molar mass of X} \]
We should substitute 3.625 g for mass of X and 1.476 g for mass of O
\[ 3.625 g = 1.476 g × \frac{1}{16 g/mol} × 2/3 × \text{ molar mass of X } \\ \text{ Molar mass } X \approx 59 \]
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Question 28 of 30
28. Question
A compound of carbon and hydrogen contains 92.3% C and has a molar mass of 78.1 g/mol. What is its molecular formula?
Correct
We start with a 100-g sample.
We divide each element’s percentage (converted to grams) by its atomic mass:
\[ C:\frac{92.3 g}{12g/mol}=7.69 \\ H:\frac{7.7 g}{1g/mol}=7.7 \]
To establish a whole-number ratio of carbon to hydrogen, divide each factor by the smallest factor. The ration of atoms is 1 to 1
\[ C:\frac{7.69}{7.69}=1 \\ H:\frac{7.7}{7.69}\approx 1 \]
The empirical formula is CH. Since the molecular mass of the compound is 78.1 amu, the sum of the mass of 1C and 1H in atomic mass units (12amu + 1amu = 13amu) must be equal to 78.1 amu. To find this number, divide 78.1 amu by 13 amu:
\( \frac{78.1}{13}=6 \text{ so the molecular formula is }C_6H_6 \)
Incorrect
We start with a 100-g sample.
We divide each element’s percentage (converted to grams) by its atomic mass:
\[ C:\frac{92.3 g}{12g/mol}=7.69 \\ H:\frac{7.7 g}{1g/mol}=7.7 \]
To establish a whole-number ratio of carbon to hydrogen, divide each factor by the smallest factor. The ration of atoms is 1 to 1
\[ C:\frac{7.69}{7.69}=1 \\ H:\frac{7.7}{7.69}\approx 1 \]
The empirical formula is CH. Since the molecular mass of the compound is 78.1 amu, the sum of the mass of 1C and 1H in atomic mass units (12amu + 1amu = 13amu) must be equal to 78.1 amu. To find this number, divide 78.1 amu by 13 amu:
\( \frac{78.1}{13}=6 \text{ so the molecular formula is }C_6H_6 \)
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Question 29 of 30
29. Question
Calculate ΔH for NO2 by using the following data.
NO (g) + O3 (g) → NO2(g) + O2(g) ΔH= – 198.9 KJ
O3 (g) → 3/2 O2 (g) ΔH= – 142.3 KJ
O2 (g) → 2O (g) ΔH= + 495.0 KJ
Correct
The enthalpy of formation (or heat of formation) ∆Hf is the enthalpy change associated with forming 1 mole of NO2 from its constituent elements in their standard state
NO (g) + O (g) → NO2(g)
We can use Hess’s law to calculate the heat of formation of NO2.
The law says: if a reaction is carried out in a number of steps, ∆H for the overall reaction is the sum of ∆H for each individual step. We want NO2 on the product side, so we reverse the second reaction. The sign of ΔH is also changed. The third reaction multiply ½
NO (g) + O3 (g) → NO2 (g) + O2 (g) ∆H = -198.9 kJ
3/2 O2 (g) → O3 (g) ∆H = +142.3 kJ
O (g) → ½ O2 (g) ∆H = -495.0/2 = -247.5 kJ
overall NO (g) + O (g) → NO2 (g)
∆H = (-198.9) + 142.3 -274.5 = -304.1 kJ
Incorrect
The enthalpy of formation (or heat of formation) ∆Hf is the enthalpy change associated with forming 1 mole of NO2 from its constituent elements in their standard state
NO (g) + O (g) → NO2(g)
We can use Hess’s law to calculate the heat of formation of NO2.
The law says: if a reaction is carried out in a number of steps, ∆H for the overall reaction is the sum of ∆H for each individual step. We want NO2 on the product side, so we reverse the second reaction. The sign of ΔH is also changed. The third reaction multiply ½
NO (g) + O3 (g) → NO2 (g) + O2 (g) ∆H = -198.9 kJ
3/2 O2 (g) → O3 (g) ∆H = +142.3 kJ
O (g) → ½ O2 (g) ∆H = -495.0/2 = -247.5 kJ
overall NO (g) + O (g) → NO2 (g)
∆H = (-198.9) + 142.3 -274.5 = -304.1 kJ
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Question 30 of 30
30. Question
Which of the following processes indicate an increase in entropy?
a) N2 (s) + 3H2(g) → 2NH3 (g)
b) NaClO3 (s) → Na+ (aq) + ClO3– (aq)
c) COCl2 (g)→ CO (g) + Cl2 (g)
Correct
Entropy is roughly related to the disorder, and gases are more disordered than the other states.
Reaction 1: The number of particles in the system decreases, i.e. there are four moles of gas reactants and only 2 moles of gas products.so the entropy is on the decline.
Reaction 2: The number of particles in the system increases, i.e. the single reactant dissociates into two ion particles. In addition, the ions in the ionic solid are organized in a rigid lattice structure whereas the ions in aqueous solutions are free to move randomly through the solvent. So the entropy is in a decrease.
The number of particles in the system increases. i.e. there is one mol of gas reactant and 2 moles of gas products. The disorder is increased more.
Incorrect
Entropy is roughly related to the disorder, and gases are more disordered than the other states.
Reaction 1: The number of particles in the system decreases, i.e. there are four moles of gas reactants and only 2 moles of gas products.so the entropy is on the decline.
Reaction 2: The number of particles in the system increases, i.e. the single reactant dissociates into two ion particles. In addition, the ions in the ionic solid are organized in a rigid lattice structure whereas the ions in aqueous solutions are free to move randomly through the solvent. So the entropy is in a decrease.
The number of particles in the system increases. i.e. there is one mol of gas reactant and 2 moles of gas products. The disorder is increased more.