Q: Which equation correctly represents the amount of heat required to raise the temperature of a substance?

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

Q: A 50.0 g sample of water is heated from 20.0\,^{\circ}\mathrm{C} to 70.0\,^{\circ}\mathrm{C}. How much heat is absorbed? (Specific heat of water = $$4.18\,\mathrm{J}/(\mathrm{g}\$$cdot^{\circ}$$\mathrm{C}))$$

$$q = 50.0 \times 4.18 \times (70.0 - 20.0) = 10,450\,\mathrm{J}$$

Question 1

Which of the following statements best describes an endothermic process?

Accepted Answer

Heat is absorbed by the system from the surroundings, and the temperature of the surroundings decreases.

Question 2

A student mixes two chemicals in a beaker and observes that the beaker feels cold to the touch. Which of the following best explains this observation?

Accepted Answer

The reaction is endothermic because heat is absorbed from the surroundings.

Question 3

Which equation correctly represents the amount of heat required to raise the temperature of a substance?

Accepted Answer

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

Question 4

A 50.0 g sample of water is heated from 20.0\,^{\circ}\mathrm{C} to 70.0\,^{\circ}\mathrm{C}. How much heat is absorbed? (Specific heat of water = $$4.18\,\mathrm{J}/(\mathrm{g}\$$cdot^{\circ}$$\mathrm{C}))$$

Accepted Answer

$$q = 50.0 	imes 4.18 	imes (70.0 - 20.0) = 10,450\,\mathrm{J}$$

Question 5

Which of the following best describes the energy changes during the melting of ice at 0\,^{\circ}\mathrm{C}?

Accepted Answer

It is an endothermic process because heat is absorbed from the surroundings.

Question 6

Which of the following is true at thermal equilibrium between a piece of metal and water?

Accepted Answer

The average kinetic energy of the metal and water are equal.

Question 7

Which of the following processes is exothermic?

Accepted Answer

Condensation of steam

Question 8

A chemical reaction has $$\Delta H = -150\,\mathrm{kJ}. $$Which statement is correct?

Accepted Answer

The reaction is exothermic and releases 150 kJ of heat.

Question 9

Which of the following best explains why the temperature of the surroundings decreases during an endothermic reaction?

Accepted Answer

Heat is absorbed by the system from the surroundings.

Question 10

A 100.0 g sample of aluminum at 100.0\,^{\circ}\mathrm{C} is placed in 50.0 g of water at 22.0\,^{\circ}\mathrm{C}. If the specific heat of aluminum is $$0.91\,\mathrm{J}/(\mathrm{g}\$$cdot^{\circ}$$\mathrm{C})$$ and water is $$4.18\,\mathrm{J}/(\mathrm{g}\$$cdot^{\circ}$$\mathrm{C})$$, what is the final temperature at equilibrium? (Assume no heat loss to the environment.)

Accepted Answer

About $$35.9\,^{\circ}\mathrm{C}$$

Question 11

Which of the following correctly describes the direction of heat flow when a hot metal is placed in cool water?

Accepted Answer

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

Question 12

Which of the following phase changes is always endothermic?

Accepted Answer

Melting

Question 13

The energy required to break one mole of H–H bonds is 436 kJ. What is the energy change when 2 moles of H–H bonds are broken?

Accepted Answer

$$872\,\mathrm{kJ}$$ absorbed

Question 14

Which of the following best describes the potential energy change in an exothermic reaction?

Accepted Answer

The potential energy of the products is lower than that of the reactants.

Question 15

Which of the following is the correct relationship according to the first law of thermodynamics in a calorimetry experiment?

Accepted Answer

The heat lost by the metal equals the heat gained by the water.

Question 16

Which of the following is NOT a characteristic of an exothermic reaction?

Accepted Answer

The enthalpy change $$\Delta H is $$positive.

Question 17

A student claims that thermal equilibrium is reached at time $$t in a $$temperature vs. time graph where the temperature levels off. Which statement best supports or refutes the claim?

Accepted Answer

The claim is correct because the temperature of both objects is constant and equal at time $$t.$$

Question 18

Which of the following best describes the energy diagram of an endothermic reaction?

Accepted Answer

The products are at a higher potential energy than the reactants.

Thermochemistry and Energy Changes in Chemical Processes

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