Question 1

The heat of combustion of methane is -50.38 kJ/mol.How many moles of methane must be burned to produce 137 kJ of heat?
A)6.90 mol
B)0.367 mol
C)2.72 mol
D)1.37 mol
E)0.272 mol

Accepted Answer

The answer of The heat of combustion of methane is...

Question 2

The complete combustion of propane,C₃H₈(g),is represented by the equation: C₃H₈(g)+ 5 O₂(g)→ 3 CO₂(g)+ 4 H₂O(l)Δ_rH° = -2220 kJ /mol How much heat is evolved in the complete combustion of 12.5 L C₃H₈(g)at 25 °C and 790 mmHg? A)8.27 × 10⁴ kJ B)1.41 × 10⁴ kJ C)653 kJ D)168 kJ E)1180 kJ

Accepted Answer

First, convert 12.5 L of C₃H₈ to moles using the ideal gas law (PV = nRT). Then, multiply the moles by the enthalpy change per mole (-2220 kJ/mol) to find the heat evolved.

Question 3

Calculate ΔU for a system that loses 475 kJ of heat and does 155 kJ of expansion work on the surroundings.
A)-630 kJ
B)-320 kJ
C)+630 kJ
D)+320 kJ

Accepted Answer

The change in internal energy (ΔU) for a system can be calculated using the first law of thermodynamics, ΔU = q + w, where q is the heat exchanged with the surroundings, and w is the work done by the system. Given that the system loses 475 kJ of heat (q = -475 kJ, since heat is lost) and does 155 kJ of expansion work on the surroundings (w = -155 kJ, since work is done by the system), ΔU = -475 kJ + (-155 kJ) = -630 kJ.

Question 4

Complete combustion of 75.0 g acetylene,C₂H₂,liberated 3750 kJ of heat.What is the heat of combustion,Δ_rH_comb,of acetylene? A)-50.0 kJ/mol B)+50.0 kJ/mol C)+1302 kJ/mol D)-1302 kJ/mol E)-0.521 kJ/mol

Accepted Answer

The heat of combustion is the amount of heat released when one mole of a substance is completely burned. Given that 75.0 g of acetylene releases 3750 kJ, we first need to calculate the moles of acetylene burned. The molar mass of acetylene (C2H2) is approximately 26.04 g/mol (12*2 + 1*2). Thus, 75.0 g corresponds to 75.0 / 26.04 ≈ 2.88 moles. The heat of combustion per mole is then 3750 kJ / 2.88 moles ≈ 1302 kJ/mol. Since combustion releases heat, the sign is negative, indicating an exothermic process. Therefore, the correct answer is -1302 kJ/mol.

Question 5

What is the work in joules done on the system to compress He gas from 24.0 L to 12.5 L against a pressure of 1.5 atm at a constant temperature of 37.4 °C? A)5.5 × 10^{3 J} B)-17 ^J C)17 ^J D)1.7 × 10^{3 J} E)-1.7 × 10^{3 J}

Accepted Answer

The answer of What is the work in joules done...

Question 6

For the reaction H₂(g)+ 1/2 O₂(g)→ H₂O(g)Δ_rH° = -241.8 kJ/mol, What quantity of heat is liberated by the reaction of 10.0 L of O₂ measured at 22.0 °C and 742 mmHg? A)120 kJ B)2610 kJ C)1310 kJ D)195 kJ E)97.5 kJ

Accepted Answer

The answer of For the reaction H₂(g)+ 1/2 O₂(g)→ H₂O(g)Δ_rH°...

Question 7

What is the heat of combustion in kJ/g of benzoic acid (C₆H₅COOH)if the initial temperature was 22.62 °C,the final temperature was 31.10 °C,the heat capacity of the bomb calorimeter was 4.88 kJ/ °C,and 1.567 grams were combusted? A)-26.4 kJ/g B)-64.8 kJ/g C)-9.99 kJ/g D)-41.4 kJ/g E)35.5 kJ/g

Accepted Answer

The heat of combustion can be calculated using the formula: heat of combustion = (heat capacity of the calorimeter * change in temperature) / mass of the substance. Here, the change in temperature is 31.10 °C - 22.62 °C = 8.48 °C. The heat absorbed by the calorimeter is 4.88 kJ/°C * 8.48 °C = 41.4 kJ. Therefore, the heat of combustion per gram of benzoic acid is -41.4 kJ / 1.567 g = -26.4 kJ/g. The negative sign indicates that heat is released during the combustion.

Question 8

For the reaction H₂(g)+ 1/2 O₂(g)→ H₂O(g)Δ_rH° = -241.8 kJ/mol, What quantity of heat,in kJ,evolved when a 72.0 g mixture containing equal parts of H₂ and O₂,by mass,is burned? A)8630 kJ B)4860 kJ C)1088 kJ D)272 kJ E)544 kJ

Accepted Answer

First, determine the molar mass of H2 and O2 to find out how many moles of each are in 36.0 g (since the mixture is equal parts by mass, each element accounts for half of the total mass, 72.0 g). The molar mass of H2 is approximately 2.02 g/mol, and for O2, it's approximately 32.00 g/mol. Thus, for H2, $36.0 \, \text{g} \div 2.02 \, \text{g/mol} = 17.82 \, \text{mol}$, and for O2, $36.0 \, \text{g} \div 32.00 \, \text{g/mol} = 1.125 \, \text{mol}$. The reaction requires 2 moles of H2 for every 1 mole of O2, but here O2 is the limiting reagent. Since the reaction consumes O2 at a rate of 0.5 moles of O2 per mole of H2O produced, 1.125 moles of O2 will produce 2.25 moles of H2O. Given the ΔH° of -241.8 kJ/mol for the reaction, the total heat evolved is $2.25 \, \text{mol} \times -241.8 \, \text{kJ/mol} = -544.05 \, \text{kJ}$, which rounds to -544 kJ.

Question 9

Two solutions,250.0 mL of 1.00 M CaCl₂(aq)and 250.0 mL of 1.00 M K₂SO₄(aq),are added to a calorimeter with a total heat capacity,after the solutions are added,of 1.25 kJ/ °C and the temperature decreased by 2.40 °C.Determine q_rxn per mole of CaSO₄(s)formed in the reaction. A)+12.0 kJ/mol B)-12.0 kJ/mol C)+6.00 kJ/mol D)-6.00 kJ/mol

Accepted Answer

The answer of Two solutions,250.0 mL of 1.00 M CaCl₂(aq)and...

Question 10

A certain reaction releases 10.1 kJ at constant volume and at constant pressure releases 8.4 kJ.What is △U for the reaction?
A)-10.1 kJ
B)-8.4 kJ
C)+8.4 kJ
D)-1.7 kJ

Accepted Answer

The change in internal energy (△U) for a reaction at constant volume is directly given by the heat released or absorbed, which is -10.1 kJ in this case.

Question 11

The complete combustion of propane,C₃H₈(g),is represented by the equation: C₃H₈(g)+ 5 O₂(g)→ 3 CO₂(g)+ 4 H₂O(l)Δ_rH° = -2220 kJ /mol How much heat is evolved in the complete combustion of 20.0 L C₃H₈(g)at STP? A)2486 kJ B)1007 kJ C)994 kJ D)1957 kJ E)495 kJ

Accepted Answer

The answer of The complete combustion of propane,C₃H₈(g),is represented by...

Question 12

Cyclohexanol,C₆H₁₂O,has a heat of combustion of -890.7 kcal/mol.A sample containing 0.708 g of cyclohexanol undergoes complete combustion in a bomb calorimeter that has a heat capacity of 2.70 kcal/ °C.What is the final temperature if the initial water temperature is 27.0 °C? A)24.7 °C B)29.3 °C C)27.4 °C D)26.6 °C E)31.4 °C

Accepted Answer

First, calculate the amount of heat released by the combustion of 0.708 g of cyclohexanol. The molar mass of cyclohexanol is approximately 100.16 g/mol. Thus, 0.708 g corresponds to 0.708 g / 100.16 g/mol = 0.00707 mol. The heat released is -890.7 kcal/mol * 0.00707 mol = -6.29 kcal. Since the calorimeter has a heat capacity of 2.70 kcal/°C, the temperature change is -6.29 kcal / 2.70 kcal/°C = -2.33°C. Therefore, the final temperature is 27.0 °C - 2.33 °C = 24.7 °C, which is not listed correctly among the options. However, the correct approach to solving the problem involves calculating the heat released and dividing by the calorimeter's heat capacity to find the temperature change. Given the options and the calculation error in the final step, the intended correct process suggests a mistake in the final calculation. Reevaluating the calculation process for accuracy is necessary.

Question 13

If 356 J of work is done by a system while it loses 289 J of heat,what is the value of 
A)+645 J
B)-645 J
C)+67 J
D)-67 J
E)+134 J

Accepted Answer

According to the First Law of Thermodynamics, the change in the internal energy of a system is equal to the heat added to the system minus the work done by the system: ΔU = Q - W. Rearranging this equation, we get: W = Q - ΔU.
In this case, the system does 356 J of work while it loses 289 J of heat. Therefore, W = 356 J and Q = -289 J (the negative sign indicates heat lost). We want to find the value of ΔU, which can be calculated as follows:
ΔU = Q - W = -289 J - 356 J = -645 J.
Since ΔU is negative, the internal energy of the system has decreased. Therefore, the best choice is B, which represents a negative value of 645 J.

Question 14

250.0 g of hot coffee at 95.0 °C are placed in a 0.2000 kg mug at 20.0 °C.The specific heat of the coffee is 4.00 J/g °C,while that of the mug is 0.80 J/g °C.Assuming no heat is lost to the surroundings,what is the final temperature of the system: mug + coffee?
A)61.7 °C
B)117 °C
C)76.0 °C
D)57.5 °C
E)84.7 °C

Accepted Answer

The answer of 250.0 g of hot coffee at 95.0...

Question 15

The complete combustion of propane,C₃H₈(g),is represented by the equation: C₃H₈(g)+ 5 O₂(g)→ 3 CO₂(g)+ 4 H₂O(l)Δ_rH° = -2220 kJ/mol How much heat is evolved in the complete combustion of 2.50 g C₃H₈(g)? A)245 kJ B)50.4 kJ C)126 kJ D)5.56 kJ E)2.22 kJ

Accepted Answer

First, we need to find the moles of propane:
n = m/M = 2.50 g / 44.1 g/mol = 0.0566 mol

Next, we use the given ΔH° to calculate the heat evolved:
ΔH = n × ΔH° = 0.0566 mol × (-2220 kJ/mol) = 125.7 kJ

Rounding to the nearest whole number, we get 126 kJ, which is answer choice C.

Question 16

A sample gives off 2505 cal when burned in a bomb calorimeter.The temperature of the calorimeter assembly increases by 2.24 °C.What is the heat capacity of the calorimeter?
A)8.92 kcal/ °C
B)1.12 kcal/ °C
C)2.51 kcal/ °C
D)5.61 kcal/ °C
E)2.65 kcal/ °C

Accepted Answer

The heat capacity of the calorimeter can be calculated using the formula: Heat capacity = Heat given off / Temperature change. Converting calories to kilocalories (2505 cal = 2.505 kcal), we get Heat capacity = 2.505 kcal / 2.24 °C = 1.12 kcal/ °C.

Question 17

5.04 × 10^-3 mole of a compound is added to 41.0 g of water in a styrofoam cup and stirred until it dissolves.The temperature of the solution changes from 23.460 °C to 23.420 °C.What is the heat of solution of the compound expressed in kJ/mol? Assume the specific heat of the solution is 4.18 J/g °C. A)-0.035 kJ/mol B)1.4 kJ/mol C)-1.4 kJ/mol D)-2.8 kJ/mol E)2.8 kJ/mol

Accepted Answer

First, calculate the amount of heat absorbed by the water using the equation: 
q = m * c * ΔT 
where q is the amount of heat absorbed, m is the mass of water, c is the specific heat of the solution, and ΔT is the change in temperature. 
Substituting the given values, we get: 
q = (41.0 g) * (4.18 J/g °C) * (-0.04 °C) = -6.83 J 
Note that the temperature decreased, so the heat absorbed is negative. 
Next, calculate the number of moles of the compound using the given amount: 
n = 5.04 × 10^-3 mol 
Finally, calculate the heat of solution, which is the amount of heat absorbed per mole of compound: 
ΔHsoln = q / n = (-6.83 J) / (5.04 × 10^-3 mol) = -1356.55 J/mol = -1.4 kJ/mol 
Note that the answer is negative because the solution is exothermic, meaning that heat is released. Therefore, the correct answer is (C).

Question 18

For the reaction H₂(g)+ 1/2 O₂(g)→ H₂O(g)Δ_rH° = -241.8 kJ/mol, What mass of H₂(g)is required to liberate 1.00 × 10³ kJ of heat? A)66.2 g B)4.17 g C)8.34 g D)2.05 g E)16.7 g

Accepted Answer

Given that ΔH° = -241.8 kJ/mol for the reaction of H₂(g) with 1/2 O₂(g) to form H₂O(g), to liberate 1.00 × 10³ kJ (or 1000 kJ) of heat, we first calculate the moles of H₂ needed using the ratio from the reaction's ΔH° value. $$1000 \, \text{kJ} \times \frac{1 \, \text{mol H₂}}{241.8 \, \text{kJ}} = 4.134 \, \text{mol H₂}$$The molar mass of H₂ (H = 1.01 g/mol) is approximately 2.02 g/mol, so:$$4.134 \, \text{mol} \times 2.02 \, \text{g/mol} = 8.35 \, \text{g}$$Therefore, approximately 8.34 g of H₂(g) is required to liberate 1000 kJ of heat.

Question 19

Many people believe that coffee 
May be cooled by placing a silver spoon 
In the coffee.If 250 ml 
Of coffee at 200 °F had a spoon at 70 °F placed in it,what would be the final Celsius temperature of the spoon and coffee,assuming that no heat is lost to the surroundings? The mass of the spoon is 35 g.
A)92.8 °C
B)72.2 °C
C)57.2 °C
D)82.0 °C
E)199 °C

Accepted Answer

The answer of Many people believe that coffee 
May be...

Question 20

246 g of hot coffee at 86.0 °C are placed in a 137 g mug at 20.0 °C.The specific heat of coffee is 4.00 J/g °C,while that of the mug is 0.752 J/g °C.Assuming no heat is lost to the surroundings,what is the final temperature of the system: mug + coffee?
A)79.7 °C
B)93.7 °C
C)98.4 °C
D)76.0 °C
E)53.0 °C

Accepted Answer

The final temperature can be found by setting the heat gained by the mug equal to the heat lost by the coffee. Using the formula $q = mc\Delta T$, where $q$ is the heat transferred, $m$ is the mass, $c$ is the specific heat, and $\Delta T$ is the change in temperature, we can set up the equation: $(m_{coffee} \cdot c_{coffee} \cdot (T_f - T_{i,coffee})) + (m_{mug} \cdot c_{mug} \cdot (T_f - T_{i,mug})) = 0$. Solving for $T_f$ gives us the final temperature close to 79.7 °C.

Quiz 7: Thermochemistry

The heat of combustion of methane is -50.38 kJ/mol.How many moles of methane must be burned to produce 137 kJ of heat?

The complete combustion of propane,C₃H₈(g) ,is represented by the equation: C₃H₈(g) + 5 O₂(g) → 3 CO₂(g) + 4 H₂O(l) Δ_rH° = -2220 kJ /mol How much heat is evolved in the complete combustion of 12.5 L C₃H₈(g) at 25 °C and 790 mmHg?

Calculate ΔU for a system that loses 475 kJ of heat and does 155 kJ of expansion work on the surroundings.

Complete combustion of 75.0 g acetylene,C₂H₂,liberated 3750 kJ of heat.What is the heat of combustion,Δ_rH_comb,of acetylene?

What is the work in joules done on the system to compress He gas from 24.0 L to 12.5 L against a pressure of 1.5 atm at a constant temperature of 37.4 °C?

For the reaction H₂(g) + 1/2 O₂(g) → H₂O(g) Δ_rH° = -241.8 kJ/mol, What quantity of heat is liberated by the reaction of 10.0 L of O₂ measured at 22.0 °C and 742 mmHg?

What is the heat of combustion in kJ/g of benzoic acid (C₆H₅COOH) if the initial temperature was 22.62 °C,the final temperature was 31.10 °C,the heat capacity of the bomb calorimeter was 4.88 kJ/ °C,and 1.567 grams were combusted?

For the reaction H₂(g) + 1/2 O₂(g) → H₂O(g) Δ_rH° = -241.8 kJ/mol, What quantity of heat,in kJ,evolved when a 72.0 g mixture containing equal parts of H₂ and O₂,by mass,is burned?

Two solutions,250.0 mL of 1.00 M CaCl₂(aq) and 250.0 mL of 1.00 M K₂SO₄(aq) ,are added to a calorimeter with a total heat capacity,after the solutions are added,of 1.25 kJ/ °C and the temperature decreased by 2.40 °C.Determine q_rxn per mole of CaSO₄(s) formed in the reaction.

A certain reaction releases 10.1 kJ at constant volume and at constant pressure releases 8.4 kJ.What is △U for the reaction?

The complete combustion of propane,C₃H₈(g) ,is represented by the equation: C₃H₈(g) + 5 O₂(g) → 3 CO₂(g) + 4 H₂O(l) Δ_rH° = -2220 kJ /mol How much heat is evolved in the complete combustion of 20.0 L C₃H₈(g) at STP?

Cyclohexanol,C₆H₁₂O,has a heat of combustion of -890.7 kcal/mol.A sample containing 0.708 g of cyclohexanol undergoes complete combustion in a bomb calorimeter that has a heat capacity of 2.70 kcal/ °C.What is the final temperature if the initial water temperature is 27.0 °C?

If 356 J of work is done by a system while it loses 289 J of heat,what is the value of

250.0 g of hot coffee at 95.0 °C are placed in a 0.2000 kg mug at 20.0 °C.The specific heat of the coffee is 4.00 J/g °C,while that of the mug is 0.80 J/g °C.Assuming no heat is lost to the surroundings,what is the final temperature of the system: mug + coffee?

The complete combustion of propane,C₃H₈(g) ,is represented by the equation: C₃H₈(g) + 5 O₂(g) → 3 CO₂(g) + 4 H₂O(l) Δ_rH° = -2220 kJ/mol How much heat is evolved in the complete combustion of 2.50 g C₃H₈(g) ?

A sample gives off 2505 cal when burned in a bomb calorimeter.The temperature of the calorimeter assembly increases by 2.24 °C.What is the heat capacity of the calorimeter?

For the reaction H₂(g) + 1/2 O₂(g) → H₂O(g) Δ_rH° = -241.8 kJ/mol, What mass of H₂(g) is required to liberate 1.00 × 10³ kJ of heat?

246 g of hot coffee at 86.0 °C are placed in a 137 g mug at 20.0 °C.The specific heat of coffee is 4.00 J/g °C,while that of the mug is 0.752 J/g °C.Assuming no heat is lost to the surroundings,what is the final temperature of the system: mug + coffee?

Quiz 7: Thermochemistry

The heat of combustion of methane is -50.38 kJ/mol.How many moles of methane must be burned to produce 137 kJ of heat?

The complete combustion of propane,C3H8(g) ,is represented by the equation: C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(l) ΔrH° = -2220 kJ /mol How much heat is evolved in the complete combustion of 12.5 L C3H8(g) at 25 °C and 790 mmHg?

Calculate ΔU for a system that loses 475 kJ of heat and does 155 kJ of expansion work on the surroundings.

Complete combustion of 75.0 g acetylene,C2H2,liberated 3750 kJ of heat.What is the heat of combustion,ΔrHcomb,of acetylene?

What is the work in joules done on the system to compress He gas from 24.0 L to 12.5 L against a pressure of 1.5 atm at a constant temperature of 37.4 °C?

For the reaction H2(g) + 1/2 O2(g) → H2O(g) ΔrH° = -241.8 kJ/mol, What quantity of heat is liberated by the reaction of 10.0 L of O2 measured at 22.0 °C and 742 mmHg?

What is the heat of combustion in kJ/g of benzoic acid (C6H5COOH) if the initial temperature was 22.62 °C,the final temperature was 31.10 °C,the heat capacity of the bomb calorimeter was 4.88 kJ/ °C,and 1.567 grams were combusted?

For the reaction H2(g) + 1/2 O2(g) → H2O(g) ΔrH° = -241.8 kJ/mol, What quantity of heat,in kJ,evolved when a 72.0 g mixture containing equal parts of H2 and O2,by mass,is burned?

Two solutions,250.0 mL of 1.00 M CaCl2(aq) and 250.0 mL of 1.00 M K2SO4(aq) ,are added to a calorimeter with a total heat capacity,after the solutions are added,of 1.25 kJ/ °C and the temperature decreased by 2.40 °C.Determine qrxn per mole of CaSO4(s) formed in the reaction.