Question 1

Which of the following best describes the First Law of Thermodynamics?

Accepted Answer

The total energy of the universe is constant; energy can neither be created nor destroyed.

Question 2

A 50.0 g block of copper at $$80.0\ ^\circ \mathrm{C} is $$placed in 100.0 g of water at $$20.0\ ^\circ \mathrm{C}. If $$the specific heat capacities are $$C_s(\mathrm{Cu}) = 0.385\ \mathrm{J/g\ ^\circ C}$$ and $$C_s(\mathrm{H_2O}) = 4.18\ \mathrm{J/g\ ^\circ C}$$, what is the final temperature at thermal equilibrium? (Assume no heat loss to surroundings.)

Accepted Answer

$$T_f \approx 21.1\ ^\circ \mathrm{C}$$

Question 3

Which of the following is an example of potential energy?

Accepted Answer

A compressed spring

Question 4

Calculate the amount of heat (in Joules) required to raise the temperature of 25.0 g of ethanol ($$C_2H_5OH) $$from $$15.0\ ^\circ \mathrm{C} to$$ $$35.0\ ^\circ \mathrm{C}. $$The specific heat capacity of ethanol is $$2.44\ \mathrm{J/g\ ^\circ C}.$$

Accepted Answer

$$q = 1220\ \mathrm{J}$$

Question 5

Which of the following statements about state functions is correct?

Accepted Answer

Internal energy is a state function because it depends only on the current state of the system.

Question 6

A chemical reaction in a bomb calorimeter causes the temperature of the calorimeter to rise by $$2.50\ ^\circ \mathrm{C}. If $$the heat capacity of the calorimeter is $$3.00\ \mathrm{kJ/\ ^\circ C}$$, what is the change in internal energy ($$\Delta E) $$for the reaction?

Accepted Answer

$$\Delta E = 7.50\ \mathrm{kJ}$$

Question 7

Which of the following best describes an exothermic reaction?

Accepted Answer

A reaction in which $$\Delta H \u003c 0$$ and heat is released to the surroundings.

Question 8

A gas expands from $$2.00\ \mathrm{L} to$$ $$5.00\ \mathrm{L}$$ against an external pressure of $$1.00\ \mathrm{atm}. $$How much work (in Joules) is done by the gas? ($$1\ \mathrm{L\cdot atm} = 101.3\ \mathrm{J})$$

Accepted Answer

$$w = +303.9\ \mathrm{J}$$

Question 9

Which of the following is an intensive property?

Accepted Answer

Specific heat capacity

Question 10

A 10.0 g sample of metal at $$100.0\ ^\circ \mathrm{C} is $$placed in 50.0 g of water at $$20.0\ ^\circ \mathrm{C}. $$The final temperature is $$22.0\ ^\circ \mathrm{C}. If $$the specific heat capacity of water is $$4.18\ \mathrm{J/g\ ^\circ C}$$, what is the specific heat capacity of the metal?

Accepted Answer

$$C_s = 0.10\ \mathrm{J/g\ ^\circ C}$$

Question 11

Which equation correctly relates the change in internal energy ($$\Delta E$$), heat ($$q$$), and work ($$w$$)?

Accepted Answer

$$\Delta E = q + w$$

Question 12

A reaction has $$q = -150\ \mathrm{J}$$ and $$w = +50\ \mathrm{J}. $$What is $$\Delta E$$ for the system?

Accepted Answer

$$\Delta E = -100\ \mathrm{J}$$

Question 13

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

Accepted Answer

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

Question 14

A 1.00 g sample of a substance is burned in a bomb calorimeter, causing the temperature to rise by $$3.00\ ^\circ \mathrm{C}. If $$the heat capacity of the calorimeter is $$5.00\ \mathrm{kJ/\ ^\circ C}$$, what is the energy released per gram of the substance?

Accepted Answer

$$15.0\ \mathrm{kJ/g}$$

Question 15

Which of the following best describes the standard enthalpy of formation ($$\Delta H_f^\circ) $$for a compound?

Accepted Answer

The enthalpy change when 1 mole of the compound forms from its elements in their standard states.

Question 16

A propane tank contains 13.2 kg of propane ($$C_3H_8). $$The enthalpy of combustion of propane is $$-2044\ \mathrm{kJ/mol}. $$How much heat (in kJ) is released when all the propane is burned? (Molar mass of $$C_3H_8 = 44.1\ \mathrm{g/mol})$$

Accepted Answer

$$-611,000\ \mathrm{kJ}$$

Question 17

Which of the following is true about heat capacity?

Accepted Answer

It is an extensive property and depends on the amount of substance.

Question 18

A reaction is carried out in a coffee cup calorimeter. Which of the following is measured directly by this experiment?

Accepted Answer

The enthalpy change ($$\Delta H) at $$constant pressure.

Question 19

Which of the following equations correctly expresses the relationship between heat, mass, specific heat capacity, and temperature change?

Accepted Answer

$$q = m C_s \Delta T$$

Chapter 7: Energy, Heat, and Thermodynamics in Chemistry

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