Q: A 50.0 g sample of iron ($$c = 0.45 \ \mathrm{J/g\cdot ^\circ C}) is $$heated from $$25.0^\circ C to$$ $$75.0^\circ C. $$How much energy is absorbed?

$$Q = 50.0 \times 0.45 \times (75.0 - 25.0) = 1125 \ \mathrm{J}$$

Q: A 10.0 g sample of copper ($$c = 0.38 \ \mathrm{J/g\cdot ^\circ C}) is $$heated from $$20.0^\circ C to$$ $$80.0^\circ C. $$How much energy is required?

$$Q = 10.0 \times 0.38 \times (80.0 - 20.0) = 228 \ \mathrm{J}$$

Q: Which of the following is the correct formula for converting Celsius to Fahrenheit?

$$^\circ F = (^\circ C \times \frac{9}{5}) + 32$$

Question 1

Which of the following best describes an exothermic reaction?

Accepted Answer

A reaction that releases heat to the surroundings, resulting in a temperature increase.

Question 2

A sample of gas has an initial pressure of 2.00 atm, a volume of 3.00 L, and a temperature of 300 K. If the volume is increased to 6.00 L and the temperature is raised to 600 K, what is the final pressure, assuming the number of moles remains constant? Use the combined gas law.

Accepted Answer

$$P_2$$ = \frac{$$P_1$$ $$V_1$$ $$T_2$$}{$$T_1$$ $$V_2$$} = \frac{2.00 	imes 3.00 	imes 600}{300 	imes 6.00} = 1.00$$ atm

Question 3

Which of the following equations correctly represents the relationship between heat ($$Q$$), mass ($$m$$), specific heat ($$c$$), and temperature change ($$\Delta T$$)?

Accepted Answer

$$Q = m \cdot c \cdot \Delta T$$

Question 4

A 50.0 g sample of iron ($$c = 0.45 \ \mathrm{J/g\cdot ^\circ C}) is $$heated from $$25.0^\circ C to$$ $$75.0^\circ C. $$How much energy is absorbed?

Accepted Answer

$$Q = 50.0 	imes 0.45 	imes (75.0 - 25.0) = 1125 \ \mathrm{J}$$

Question 5

Which of the following is NOT a standard unit for measuring pressure?

Accepted Answer

Joule

Question 6

A reaction absorbs 150 J of heat and does 50 J of work on the surroundings. What is the change in internal energy ($$\Delta E) of $$the system?

Accepted Answer

$$\Delta E = q + w = 150 + (-50) = 100 \ \mathrm{J}$$

Question 7

Which of the following statements about endothermic and exothermic reactions is correct?

Accepted Answer

Endothermic reactions absorb energy from the surroundings.

Question 8

Convert $$25.0^\circ C to $$Kelvin.

Accepted Answer

$$K = 25.0 + 273.15 = 298.15 \ \mathrm{K}$$

Question 9

Which of the following best describes Hess' Law?

Accepted Answer

The enthalpy change of a reaction depends only on the initial and final states, not the path taken.

Question 10

A 10.0 g sample of copper ($$c = 0.38 \ \mathrm{J/g\cdot ^\circ C}) is $$heated from $$20.0^\circ C to$$ $$80.0^\circ C. $$How much energy is required?

Accepted Answer

$$Q = 10.0 	imes 0.38 	imes (80.0 - 20.0) = 228 \ \mathrm{J}$$

Question 11

Which of the following is the correct formula for converting Celsius to Fahrenheit?

Accepted Answer

$$^\circ F = (^\circ C 	imes \frac{9}{5}) + 32$$

Question 12

A chemical reaction has $$q = -50 \ \mathrm{J}$$ and $$w = +20 \ \mathrm{J}. $$What is $$\Delta E$$ and is the process endothermic or exothermic?

Accepted Answer

$$\Delta E = -30 \ \mathrm{J}$$, exothermic

Question 13

Which of the following is a correct application of the ideal gas law?

Accepted Answer

$$PV = nRT$$

Question 14

A 2.00 L sample of gas at 1.00 atm and 300 K is compressed to 1.00 L at constant temperature. What is the final pressure?

Accepted Answer

$$P_2$$ = \frac{$$P_1$$ $$V_1$$}{$$V_2$$} = \frac{1.00 	imes 2.00}{1.00} = 2.00$$ atm

Question 15

Which of the following is a real-life example of an endothermic process?

Accepted Answer

Melting of ice in a drink.

Question 16

If 100.0 J of heat is added to 20.0 g of water ($$c = 4.19 \ \mathrm{J/g\cdot ^\circ C}$$), what is the temperature change?

Accepted Answer

$$\Delta T = \frac{Q}{m c} = \frac{100.0}{20.0 	imes 4.19} = 1.19^\circ C$$

Question 17

Which of the following is the correct expression for the change in enthalpy ($$\Delta H) $$for a reaction using Hess' Law?

Accepted Answer

$$\Delta H_{rxn} = \sum \Delta H_{products} - \sum \Delta H_{reactants}$$

Guidance for Using the Gas Law Information Matrix

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