Q: Which equation correctly relates heat ($$q$$), mass ($$m$$), specific heat capacity ($$C_s$$), and temperature change ($$\Delta T$$)?

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

Question 1

Which statement best describes the law of conservation of energy as discussed by Richard Feynman?

Accepted Answer

Energy is a quantity that remains constant in all natural phenomena; it can change form but cannot be created or destroyed.

Question 2

A combustion reaction for methane is given by: $$\mathrm{CH_4$(g) + 2\ O_2$(g) \rightarrow CO_2$(g) + 2\ H_2O(g)}$$ with $$\Delta H^\circ_{rxn} = -802\ \mathrm{kJ}. $$What does the negative sign of $$\Delta H^\circ_{rxn}$$ indicate?

Accepted Answer

The reaction releases heat to the surroundings.

Question 3

Which of the following is NOT a state function?

Accepted Answer

Work ($$w)$$

Question 4

A system absorbs 655 J of heat and does 344 J of work on the surroundings. What is the change in internal energy ($$\Delta E) of $$the system?

Accepted Answer

$$\Delta E = 311\ \mathrm{J}$$

Question 5

Which of the following best describes an open system in thermochemistry?

Accepted Answer

A system where both energy and matter are exchanged with the surroundings.

Question 6

A 25 g sample of gold ($$C_s = 0.128\ \mathrm{J/g\ ^\circ C}) is $$initially at $$27.0\ ^\circ C. If it $$absorbs $$2.35\ \mathrm{kJ} of $$heat, what is its final temperature?

Accepted Answer

$$T_f = 94.0\ ^\circ C$$

Question 7

Which equation correctly relates heat ($$q$$), mass ($$m$$), specific heat capacity ($$C_s$$), and temperature change ($$\Delta T$$)?

Accepted Answer

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

Question 8

A block of silver ($$C_s = 0.235\ \mathrm{J/g\ ^\circ C}) at$$ $$58.5\ ^\circ C is $$placed in $$100\ \mathrm{g} of $$water ($$C_s = 4.18\ \mathrm{J/g\ ^\circ C}) at$$ $$24.8\ ^\circ C. $$The final temperature is $$26.2\ ^\circ C. $$What is the mass of the silver block?

Accepted Answer

$$m_{Ag} = 75\ \mathrm{g}$$

Question 9

Which of the following statements about standard enthalpy of formation ($$\Delta H_f^\circ) is $$TRUE?

Accepted Answer

It is the enthalpy change for forming 1 mole of a compound from its elements in their standard states.

Question 10

A refrigerator uses $$745\ \mathrm{kWh} of $$electrical energy per year. Express this amount in $$\mathrm{kJ}.$$

Accepted Answer

$$2,682,000\ \mathrm{kJ}$$

Question 11

Which of the following reactions is an example of an endothermic process?

Accepted Answer

A reaction where $$\Delta H \u003e 0$$ and heat is absorbed by the system.

Question 12

If a chemical system releases $$622\ \mathrm{kJ} of $$heat and does $$105\ \mathrm{kJ} of $$work on the surroundings, what is $$\Delta E$$ for the system?

Accepted Answer

$$\Delta E = -727\ \mathrm{kJ}$$

Question 13

Which formula is used to calculate the work done by a system during expansion against a constant external pressure?

Accepted Answer

$$w = -P_{ext} \Delta V$$

Question 14

A fuel burns at constant pressure, producing $$3452\ \mathrm{kJ} of $$heat and $$21\ \mathrm{kJ} of $$work. What are $$\Delta E$$ and $$\Delta H$$ for the combustion?

Accepted Answer

$$\Delta E = 3431\ \mathrm{kJ}$$, $$\Delta H = 3452\ \mathrm{kJ}$$

Question 15

Which of the following best explains why fossil fuel combustion contributes to global warming?

Accepted Answer

It releases $$\mathrm{CO_2$}$$, a greenhouse gas, into the atmosphere.

Question 16

Which statement about standard states is correct?

Accepted Answer

A pure gas at exactly $$1\ \mathrm{atm}$$ pressure is in its standard state.

Question 17

Which equation is used to calculate the standard enthalpy change of a reaction ($$\Delta H^\circ_{rxn}) $$from standard enthalpies of formation?

Accepted Answer

$$\Delta H^\circ_{rxn} = \sum n \Delta H_f^\circ (	ext{products}) - \sum n \Delta H_f^\circ (	ext{reactants})$$

Question 18

If the reaction $$A + 2B \rightarrow C + 3D$$ has $$\Delta H = 155\ \mathrm{kJ}$$, what is $$\Delta H$$ for the reverse reaction?

Accepted Answer

$$\Delta H = -155\ \mathrm{kJ}$$

General Chemistry: Thermochemistry (Chapter 7) Study Notes

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