Q: A 1.0215 g sample of benzoic acid ($\mathrm{C_7H_6O_2}$, MM = 122.12 g/mol) is combusted in a bomb calorimeter, causing the temperature to rise by $2.538\ ^\circ\mathrm{C}$. If the heat of combustion is $-3222.0\ \mathrm{kJ/mol}$, what is the heat capacity of the calorimeter?

$C_{cal} = \frac{m_{BA} \Delta U_{BA}}{MM_{BA} \Delta T}$

Q: Which of the following best explains why $\Delta H$ and $\Delta U$ are not always equal for a chemical reaction?

Because $\Delta H$ includes the $P\Delta V$ work term, which is not always zero.

Q: Which of the following is true about the calibration of a bomb calorimeter?

It is done by combusting a substance with a known heat of combustion.

Q: Which of the following correctly describes an exothermic reaction?

$\Delta H < 0$ and heat is released to the surroundings.

Q: Which of the following is NOT a property of a state function?

Its value is determined by the process used to reach the state.

Question 1

Which of the following best describes why the work done by a system during expansion at constant pressure is negative?

Accepted Answer

Because the system is losing energy to the surroundings as it does work.

Question 2

A reaction occurs in a bomb calorimeter (constant volume) and releases heat. Which equation correctly relates the change in internal energy to the heat measured?

Accepted Answer

$\Delta U = q_v$

Question 3

Which of the following is a state function?

Accepted Answer

Enthalpy ($H$)

Question 4

During the combustion of methane at constant pressure, the following reaction occurs: $\mathrm{CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(l)}$. If the temperature is $298\ \mathrm{K}$ and $R = 8.314\ \mathrm{J\ mol^{-1}\ K^{-1}}$, what is the work done by the system per mole of methane?

Accepted Answer

$w = -(1-3)RT = 4.96\ \mathrm{kJ}$

Question 5

Which of the following statements about enthalpy ($H$) is correct?

Accepted Answer

Enthalpy is defined as $H = U + PV$.

Question 6

A bomb calorimeter is used to measure the heat of combustion of a substance. Which of the following is true about the process?

Accepted Answer

The reaction occurs at constant volume and no work is done.

Question 7

If a reaction in a coffee cup calorimeter (constant pressure) causes the temperature of the water to increase, which of the following is true?

Accepted Answer

The reaction is exothermic and $\Delta H < 0$.

Question 8

Which equation correctly relates the heat absorbed or released by a substance to its mass, specific heat, and temperature change?

Accepted Answer

$q = mC\Delta T$

Question 9

A 1.0215 g sample of benzoic acid ($\mathrm{C_7H_6O_2}$, MM = 122.12 g/mol) is combusted in a bomb calorimeter, causing the temperature to rise by $2.538\ ^\circ\mathrm{C}$. If the heat of combustion is $-3222.0\ \mathrm{kJ/mol}$, what is the heat capacity of the calorimeter?

Accepted Answer

$C_{cal} = \frac{m_{BA} \Delta U_{BA}}{MM_{BA} \Delta T}$

Question 10

Which of the following best explains why $\Delta H$ and $\Delta U$ are not always equal for a chemical reaction?

Accepted Answer

Because $\Delta H$ includes the $P\Delta V$ work term, which is not always zero.

Question 11

A chemical reaction at constant pressure absorbs 150 J of heat and does 50 J of work on the surroundings. What is the change in internal energy ($\Delta U$)?

Accepted Answer

$\Delta U = 100\ \mathrm{J}$

Question 12

Which of the following is true about the calibration of a bomb calorimeter?

Accepted Answer

It is done by combusting a substance with a known heat of combustion.

Question 13

Which of the following correctly describes an exothermic reaction?

Accepted Answer

$\Delta H < 0$ and heat is released to the surroundings.

Question 14

A reaction occurs in a system at constant pressure. Which equation relates the change in enthalpy to the heat exchanged?

Accepted Answer

$\Delta H = q_p$

Question 15

Which of the following is NOT a property of a state function?

Accepted Answer

Its value is determined by the process used to reach the state.

Question 16

In a bomb calorimeter experiment, why is it important that the calorimeter is insulated from the surroundings?

Accepted Answer

To ensure that all the heat produced by the reaction is transferred to the water in the calorimeter.

Question 17

Which of the following best describes the difference between $q_p$ and $q_v$?

Accepted Answer

$q_p$ is the heat at constant pressure, $q_v$ is the heat at constant volume.

Question 18

A reaction in a bomb calorimeter causes the temperature of the calorimeter to increase by $5.00\ ^\circ\mathrm{C}$. If the heat capacity of the calorimeter is $10.0\ \mathrm{kJ}/^\circ\mathrm{C}$, what is the total heat released by the reaction?

Accepted Answer

$q = 50.0\ \mathrm{kJ}$

Question 19

Which of the following scenarios would result in $\Delta H = \Delta U$ for a chemical reaction?

Accepted Answer

The reaction occurs with no change in the number of moles of gas.

Chapter 6.3: Thermochemistry – Work, Internal Energy, and Calorimetry

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