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

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

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

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

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 $\Delta H > 0$ 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

Study Guide - Practice Questions

Study Guide - Flashcards