Q: A refrigerator uses 780 kWh of electrical energy per year. How many kilocalories of electricity does it use in three years? ($$1\ \mathrm{kWh} = 3.60 \times 10^6$\ \mathrm{J}$$, $$1\ \mathrm{cal} = 4.184\ \mathrm{J})$$

$$\text{Total energy} = 780\ \mathrm{kWh} \times 3 = 2340\ \mathrm{kWh}$$ $$= 2340 \times 3.60 \times 10^6$\ \mathrm{J} = 8.424 \times 10^9$\ \mathrm{J}$$ $$= \frac{8.424 \times 10^9$\ \mathrm{J}}{4.184 \times 10^3$\ \mathrm{J/kcal}} = 2.01 \times 10^6$\ \mathrm{kcal}$$

Q: A gas expands in a container, increasing the volume from 4.3 L to 8.2 L at a constant pressure of 931 mmHg. If the system absorbs 2.3 kJ of energy, what is the internal energy change ($$\Delta E) of $$the system? ($$1\ \mathrm{L} \cdot \mathrm{atm} = 101.3\ \mathrm{J}$$, $$1\ \mathrm{atm} = 760\ \mathrm{mmHg})$$

$$w = -P\Delta V = -\left(\frac{931}{760}\ \mathrm{atm}\right)(8.2-4.3)\ \mathrm{L} \times 101.3\ \mathrm{J/L\cdot atm} = -505\ \mathrm{J}$$ $$\Delta E = q + w = 2300\ \mathrm{J} + (-505\ \mathrm{J}) = 1795\ \mathrm{J}$$

Question 1

Which of the following best describes the difference between a compound and a mixture?

Accepted Answer

A compound is composed of two or more elements chemically bonded together, while a mixture is composed of elements and/or compounds physically mixed together.

Question 2

Which of the following is an example of a homogeneous mixture?

Accepted Answer

Soda

Question 3

Which of the following represents a chemical change?

Accepted Answer

Cooking an egg

Question 4

Which of the following is a physical property?

Accepted Answer

Mercury is a silvery liquid at 25ºC.

Question 5

Which of the following is NOT an intensive property?

Accepted Answer

Milligrams

Question 6

Which of the following is an extensive property?

Accepted Answer

Moles

Question 7

Which of the following statements about the Law of Conservation of Mass is correct?

Accepted Answer

The total mass of reactants equals the total mass of products.

Question 8

A sample of copper absorbs 3.53 kJ of heat, which increases the temperature by 25 ºC. If the specific heat capacity of copper is $$0.385\ \mathrm{J}/\mathrm{g}\cdot{}^{\circ}\mathrm{C}$$, what is the mass of the copper sample in kg?

Accepted Answer

$$m = \frac{q}{c\Delta T} = \frac{3530\ \mathrm{J}}{0.385\ \mathrm{J}/\mathrm{g}\cdot{}^{\circ}\mathrm{C} 	imes 25\ ^{\circ}\mathrm{C}} = 367\ \mathrm{g} = 0.367\ \mathrm{kg}$$

Question 9

Which of the following processes is endothermic?

Accepted Answer

Water boiling

Question 10

A refrigerator uses 780 kWh of electrical energy per year. How many kilocalories of electricity does it use in three years? ($$1\ \mathrm{kWh} = 3.60 	imes 10^6$\ \mathrm{J}$$, $$1\ \mathrm{cal} = 4.184\ \mathrm{J})$$

Accepted Answer

$$	ext{Total energy} = 780\ \mathrm{kWh} 	imes 3 = 2340\ \mathrm{kWh}$$ 
$$= 2340 	imes 3.60 	imes 10^6$\ \mathrm{J} = 8.424 	imes 10^9$\ \mathrm{J}$$ 
$$= \frac{8.424 	imes 10^9$\ \mathrm{J}}{4.184 	imes 10^3$\ \mathrm{J/kcal}} = 2.01 	imes 10^6$\ \mathrm{kcal}$$

Question 11

Which of the following best describes what happens during an exothermic reaction?

Accepted Answer

The system releases heat to the surroundings and feels warm to the touch.

Question 12

Which of the following is true about the direction of heat flow?

Accepted Answer

Heat always flows from a hotter object to a colder object.

Question 13

A gas expands in a container, increasing the volume from 4.3 L to 8.2 L at a constant pressure of 931 mmHg. If the system absorbs 2.3 kJ of energy, what is the internal energy change ($$\Delta E) of $$the system? ($$1\ \mathrm{L} \cdot \mathrm{atm} = 101.3\ \mathrm{J}$$, $$1\ \mathrm{atm} = 760\ \mathrm{mmHg})$$

Accepted Answer

$$w = -P\Delta V = -\left(\frac{931}{760}\ \mathrm{atm}ight)(8.2-4.3)\ \mathrm{L} 	imes 101.3\ \mathrm{J/L\cdot atm} = -505\ \mathrm{J}$$ 
$$\Delta E = q + w = 2300\ \mathrm{J} + (-505\ \mathrm{J}) = 1795\ \mathrm{J}$$

Question 14

Which of the following best describes thermal equilibrium?

Accepted Answer

When two substances in contact reach the same temperature and no longer exchange heat.

Question 15

Which of the following is a chemical property?

Accepted Answer

Reactivity with acids

Question 16

Which of the following statements about specific heat capacity is correct?

Accepted Answer

Specific heat capacity is the amount of heat required to raise the temperature of 1 gram of a substance by 1 K.

Question 17

Which of the following best describes what happens to intermolecular attractions during the phase change from solid to gas?

Accepted Answer

Intermolecular attractions decrease.

Matter and Energy: Classification, Properties, and Thermochemistry

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