Q: Which formula is used to calculate the heat absorbed or released by a substance given its mass, specific heat, and temperature change?

$$q = m \times C_s \times \Delta T$$

Question 1

Which of the following best describes the energy transformation occurring when a piece of wood is burned in a campfire?

Accepted Answer

Chemical potential energy in the wood is converted to heat and light energy.

Question 2

A gas expands against a constant external pressure of $$2.00\ \mathrm{atm}$$ from $$5.00\ \mathrm{L} to$$ $$10.00\ \mathrm{L}. $$Calculate the work done by the gas. ($$1\ \mathrm{L\ atm} = 101.3\ \mathrm{J})$$

Accepted Answer

$$w = -1013\ \mathrm{J}$$

Question 3

Which of the following is an example of an open system?

Accepted Answer

A reaction in an open beaker where gas escapes.

Question 4

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

Accepted Answer

$$\Delta U = q + w$$

Question 5

A 100 g sample of water is heated from $$20.0\ ^\circ\mathrm{C} to$$ $$80.0\ ^\circ\mathrm{C}. ($$Specific heat of water $$= 4.18\ \mathrm{J\ g$$^{-1}$$\ K$$^{-1}$$}) $$How much heat is absorbed?

Accepted Answer

$$q = 25,080\ \mathrm{J}$$

Question 6

Which of the following statements about state functions is correct?

Accepted Answer

Internal energy ($$U) $$and enthalpy ($$H) $$are state functions.

Question 7

Which process is exothermic?

Accepted Answer

Condensation of steam

Question 8

Given the following reactions and enthalpy changes:

$$\mathrm{CH_4$(g) + 2O_2(g) \rightarrow CO_2$(g) + 2H_2O(l)}\ \Delta H_1$ = -890\ \mathrm{kJ}$$

$$\mathrm{2CO(g) + O_2$(g) \rightarrow 2CO_2(g)}\ \Delta H_2$ = -566\ \mathrm{kJ}$$

Calculate $$\Delta H$$ for:
$$2\mathrm{CH_4$(g) + 3O_2(g) \rightarrow 2CO(g) + 4H_2O(l)}$$

Accepted Answer

$$\Delta H = -1214\ \mathrm{kJ}$$

Question 9

Which of the following best explains why a bathtub of water at $$40^\circ\mathrm{C}$$ contains more thermal energy than a cup of water at $$90^\circ\mathrm{C}$$?

Accepted Answer

Thermal energy depends on both temperature and mass.

Question 10

Which of the following is true for an endothermic reaction at constant pressure?

Accepted Answer

$$\Delta H \u003e 0$$ and heat is absorbed from the surroundings.

Question 11

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

Accepted Answer

It is an isolated system.

Question 12

Which formula is used to calculate the heat absorbed or released by a substance given its mass, specific heat, and temperature change?

Accepted Answer

$$q = m 	imes C_s 	imes \Delta T$$

Question 13

Which of the following is NOT a type of kinetic energy motion in molecules?

Accepted Answer

Electrostatic potential motion

Question 14

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

Accepted Answer

Zero

Question 15

Which of the following best describes the law of conservation of energy?

Accepted Answer

Energy is neither created nor destroyed, only transformed.

Question 16

A 0.250 g sample of diamond is burned in a bomb calorimeter with a heat capacity of $$6.52\ \mathrm{kJ\ ^\circ C$$^{-1}$$}. $$The temperature rises by $$1.26\ ^\circ C. $$What is the total heat released?

Accepted Answer

$$q = 8.22\ \mathrm{kJ}$$

Question 17

Which of the following is true about the sign conventions for $$q$$ and $$w in $$thermochemistry?

Accepted Answer

$$q is $$positive when heat is gained by the system; $$w is $$positive when work is done on the system.

Question 18

Which of the following best describes the difference between heat capacity ($$C) $$and specific heat ($$C_s$$)?

Accepted Answer

Heat capacity is for the whole object; specific heat is per gram.

Thermochemistry: Energy, Heat, and Enthalpy in Chemical Systems

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