Question 1

Which of the following best describes an exothermic reaction?

Accepted Answer

A reaction in which the system releases heat to the surroundings.

Question 2

A 50.0 g sample of water is heated from 25.0°C to 75.0°C. The specific heat capacity of water is $$4.18 \ \mathrm{J/g \cdot ^\circ C}. $$How much heat ($$q) is $$absorbed by the water?

Accepted Answer

$$q = 10,450 \ \mathrm{J}$$

Question 3

Which of the following is a state function?

Accepted Answer

The enthalpy change ($$\Delta H) $$for the combustion of methane.

Question 4

A system absorbs 200 kJ of heat from the surroundings and does 75 kJ of work on the surroundings. What is the change in internal energy ($$\Delta E) of $$the system?

Accepted Answer

$$\Delta E = 125 \ \mathrm{kJ}$$

Question 5

Which of the following best describes the difference between an open, closed, and isolated system?

Accepted Answer

An isolated system exchanges neither matter nor energy with the surroundings.

Question 6

Calculate the work done (in J) when a gas expands from 2.00 L to 5.00 L against a constant external pressure of 1.50 atm. ($$1 \ \mathrm{L \cdot atm} = 101.3 \ \mathrm{J})$$

Accepted Answer

$$w = -455.9 \ \mathrm{J}$$

Question 7

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

Accepted Answer

$$\Delta H is $$the heat transferred at constant pressure.

Question 8

A 25.0 g piece of metal at 100.0°C is placed in 100.0 g of water at 25.0°C. The final temperature of the system is 28.0°C. If the specific heat of water is $$4.18 \ \mathrm{J/g \cdot ^\circ C}$$, what is the specific heat capacity ($$c_s) of $$the metal? (Assume no heat loss to surroundings.)

Accepted Answer

$$c_s = 0.50 \ \mathrm{J/g \cdot ^\circ C}$$

Question 9

Which of the following reactions is endothermic?

Accepted Answer

Melting of ice to form liquid water.

Question 10

The standard enthalpy of formation ($$\Delta H_f^\circ) of an $$element in its standard state is:

Accepted Answer

$$\Delta H_f^\circ = 0 \ \mathrm{kJ/mol}$$

Question 11

Which of the following best explains why water is used as a coolant in car radiators?

Accepted Answer

Water has a high specific heat capacity.

Question 12

A chemical reaction occurs in a coffee-cup calorimeter. The temperature of 200.0 g of solution increases by 3.00°C. If the specific heat of the solution is $$4.18 \ \mathrm{J/g \cdot ^\circ C}$$, what is the heat change ($$q) $$for the reaction?

Accepted Answer

$$q = +2,508 \ \mathrm{J}$$

Question 13

Which of the following is the correct relationship between enthalpy change ($$\Delta H) $$and internal energy change ($$\Delta E) $$for a reaction at constant pressure?

Accepted Answer

$$\Delta H = \Delta E + P\Delta V$$

Question 14

Which of the following best describes the process of calorimetry?

Accepted Answer

Measuring the heat flow accompanying a chemical reaction.

Question 15

A 4.00 g sample of a substance is burned in a bomb calorimeter, causing the temperature of the calorimeter to rise by 5.00°C. If the heat capacity of the calorimeter is $$7.80 \ \mathrm{kJ/ ^\circ C}$$, what is the heat of combustion per gram of the substance?

Accepted Answer

$$q = 9.75 \ \mathrm{kJ/g}$$

Question 16

Which of the following is true regarding Hess's Law?

Accepted Answer

The enthalpy change of a reaction is the sum of the enthalpy changes of the steps into which the reaction can be divided.

Question 17

Which of the following best describes the main form of potential energy in chemistry?

Accepted Answer

Electrostatic potential energy

Question 18

A 0.500 g sample of NaCl absorbs 22.18 kJ of heat. If the specific heat of NaCl is $$0.505 \ \mathrm{J/g \cdot ^\circ C}$$ and the initial temperature is 20.0°C, what is the final temperature of the NaCl?

Accepted Answer

Final temperature = $$109,900 \ ^\circ \mathrm{C}$$

Thermochemistry: Energy, Work, and Heat in Chemical Systems

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