Q: A 32.2 g iron rod at $$22.4\ ^\circ\mathrm{C} is $$placed in water at $$63.0\ ^\circ\mathrm{C}. $$The final temperature is $$58.6\ ^\circ\mathrm{C}. If$$ $$C_s($$iron) = $$0.449\ \mathrm{J}/(g\ ^\circ\mathrm{C})$$ and $$C_s($$water) = $$4.18\ \mathrm{J}/(g\ ^\circ\mathrm{C})$$, what is the mass of water?

$$m_{\text{water}} = 32.2\ \mathrm{g} \times \frac{0.449\times(58.6-22.4)}{4.18\times(63.0-58.6)}$$

Q: Calculate the amount of heat required to raise the temperature of 26.0 g of water from $$18.0\ ^\circ\mathrm{C} to$$ $$56.0\ ^\circ\mathrm{C}$$ ($$C_s$$ for water = $$4.18\ \mathrm{J}/(g\ ^\circ\mathrm{C})).$$

$$q = 26.0 \times 4.18 \times (56.0-18.0) = 4126\ \mathrm{J}$$

Q: Which of the following is the correct formula for calculating the heat absorbed or released by a substance?

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

Question 1

Which of the following best describes the difference between kinetic energy and potential energy, as illustrated by a ball held above a table and then dropped?

Accepted Answer

Kinetic energy is the energy of motion, while potential energy is the energy stored due to position.

Question 2

A white billiard ball with 5.0 J of kinetic energy collides with a purple ball on a smooth table. After the collision, the white ball stops and the purple ball moves away. If 0.5 J of energy is lost as heat, how much kinetic energy does the purple ball have after the collision?

Accepted Answer

$$4.5\ \mathrm{J}$$

Question 3

Which of the following equations correctly expresses the relationship between work, pressure, and volume change for a gas expanding against a constant external pressure?

Accepted Answer

$$w = -P\Delta V$$

Question 4

A system absorbs 563 J of heat from the surroundings and does 498 J of work on the surroundings. What is the change in internal energy ($$\Delta E) of $$the system?

Accepted Answer

$$\Delta E = 65\ \mathrm{J}$$

Question 5

Which of the following statements about state functions is correct?

Accepted Answer

State functions depend only on the initial and final states, not on the path taken.

Question 6

A 32.2 g iron rod at $$22.4\ ^\circ\mathrm{C} is $$placed in water at $$63.0\ ^\circ\mathrm{C}. $$The final temperature is $$58.6\ ^\circ\mathrm{C}. If$$ $$C_s($$iron) = $$0.449\ \mathrm{J}/(g\ ^\circ\mathrm{C})$$ and $$C_s($$water) = $$4.18\ \mathrm{J}/(g\ ^\circ\mathrm{C})$$, what is the mass of water?

Accepted Answer

$$m_{	ext{water}} = 32.2\ \mathrm{g} 	imes \frac{0.449	imes(58.6-22.4)}{4.18	imes(63.0-58.6)}$$

Question 7

Which of the following best explains why water is used as a coolant in car engines?

Accepted Answer

Water has a high specific heat capacity, allowing it to absorb a lot of heat with little temperature change.

Question 8

A chemical reaction in a flask absorbs heat from the surroundings. What happens to the temperature of the flask?

Accepted Answer

The temperature falls.

Question 9

Which of the following is true for an exothermic reaction?

Accepted Answer

$$\Delta H is $$negative and heat is released to the surroundings.

Question 10

Calculate the amount of heat required to raise the temperature of 26.0 g of water from $$18.0\ ^\circ\mathrm{C} to$$ $$56.0\ ^\circ\mathrm{C}$$ ($$C_s$$ for water = $$4.18\ \mathrm{J}/(g\ ^\circ\mathrm{C})).$$

Accepted Answer

$$q = 26.0 	imes 4.18 	imes (56.0-18.0) = 4126\ \mathrm{J}$$

Question 11

A cylinder expands from 1.00 L to 2.00 L against an external pressure of 1.00 atm. How much work (in Joules) is done by the system? ($$1\ \mathrm{L\cdot atm} = 101.3\ \mathrm{J})$$

Accepted Answer

$$w = -101\ \mathrm{J}$$

Question 12

Which of the following is the correct formula for calculating the heat absorbed or released by a substance?

Accepted Answer

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

Question 13

Which of the following statements about the law of conservation of energy is correct?

Accepted Answer

Energy cannot be created nor destroyed, only transferred or transformed.

Question 14

A reaction has $$\Delta H = -2044\ \mathrm{kJ}$$ for the combustion of 1 mol of propane ($$\mathrm{C_3H_8}). $$How much heat is released when 2 mol of propane combust?

Accepted Answer

$$-4090\ \mathrm{kJ}$$

Question 15

Which of the following is true about the standard enthalpy of formation ($$\Delta H_f^\circ) $$for a pure element in its standard state?

Accepted Answer

$$\Delta H_f^\circ is $$zero.

Question 16

Given the reaction $$2A \rightarrow AA$$ with $$\Delta H = -51.0\ \mathrm{J}$$, what is the heat associated with the reaction of 6 moles of A?

Accepted Answer

$$-153\ \mathrm{J}$$

Question 17

Which of the following best describes the energy transfer when a hot metal block is placed in cool water?

Accepted Answer

Heat flows from the metal to the water until both reach the same temperature.

Question 18

Which of the following is NOT a form of kinetic energy?

Accepted Answer

Chemical energy

Question 19

If a reaction is reversed, what happens to the sign of $$\Delta H$$?

Accepted Answer

It changes sign.

Chapter 7: Thermochemistry – Energy, Heat, and Chemical Reactions

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