Q: A 2.0 kg block of copper (specific heat capacity $$c = 385\ \mathrm{J\ kg$$^{-1}$$\ K$$^{-1}$$}) is $$heated from $$20^\circ\mathrm{C} to$$ $$80^\circ\mathrm{C}. $$How much heat energy is absorbed by the copper block?

$$Q = 2.0 \times 385 \times (80 - 20) = 46,200\ \mathrm{J}$$

Question 1

Which of the following best describes an isolated thermodynamic system?

Accepted Answer

A system that does not exchange either energy or matter with its surroundings.

Question 2

A 2.0 kg block of copper (specific heat capacity $$c = 385\ \mathrm{J\ kg$$^{-1}$$\ K$$^{-1}$$}) is $$heated from $$20^\circ\mathrm{C} to$$ $$80^\circ\mathrm{C}. $$How much heat energy is absorbed by the copper block?

Accepted Answer

$$Q = 2.0 	imes 385 	imes (80 - 20) = 46,200\ \mathrm{J}$$

Question 3

Which statement correctly distinguishes between the latent heat of fusion and the latent heat of vaporization?

Accepted Answer

Latent heat of fusion is the energy required for a substance to change from solid to liquid, while latent heat of vaporization is for liquid to gas.

Question 4

A greenhouse uses water to moderate temperature because water has a high specific heat capacity. Which of the following best explains this effect?

Accepted Answer

Water absorbs a large amount of heat with only a small increase in temperature, helping to stabilize the greenhouse temperature.

Question 5

During a calorimetry experiment, 100 g of ice at $$0^\circ\mathrm{C} is $$added to 200 g of water at $$30^\circ\mathrm{C}. $$Assuming no heat loss to the surroundings, what is the final temperature after all the ice has melted? (Specific heat of water $$= 4,200\ \mathrm{J\ kg$$^{-1}$$\ K$$^{-1}$$}$$, latent heat of fusion of ice $$= 334,000\ \mathrm{J\ kg$$^{-1}$$})$$

Accepted Answer

The final temperature is $$0^\circ\mathrm{C}$$ because all the energy from the warm water is used to melt the ice, with no energy left to raise the temperature.

Question 6

Which of the following best describes an exothermic reaction?

Accepted Answer

A reaction in which $$\Delta H \u003c 0$$ and energy is released to the surroundings.

Question 7

A chemical reaction has an activation energy of $$50\ \mathrm{kJ\ $$mol^{-1}$$}. A $$catalyst is added, lowering the activation energy to $$20\ \mathrm{kJ\ $$mol^{-1}$$}. $$What is the effect of the catalyst on the reaction?

Accepted Answer

The catalyst increases the rate of reaction by providing an alternative pathway with lower activation energy.

Question 8

Which of the following factors does NOT affect the value of the equilibrium constant $$K_c$$ for a given reaction?

Accepted Answer

Concentration of reactants

Question 9

For the reaction $$\mathrm{N_2$}(g) + 3\mathrm{H_2$}(g) \rightleftharpoons 2\mathrm{NH_3$}(g)$$, which of the following is the correct expression for the equilibrium constant $$K_c$$?

Accepted Answer

$$K_c = \dfrac{[\mathrm{NH_3$}]^2}{[\mathrm{N_2$}][\mathrm{H_2$}]^3}$$

Question 10

According to Le Chatelier's principle, what will happen to the position of equilibrium if the pressure is increased for the reaction $$\mathrm{N_2$}(g) + 3\mathrm{H_2$}(g) \rightleftharpoons 2\mathrm{NH_3$}(g)$$?

Accepted Answer

The equilibrium will shift to the right, favoring the formation of $$\mathrm{NH_3$}.$$

Question 11

Which of the following best defines a catalyst in a chemical reaction?

Accepted Answer

A substance that increases the rate of a chemical reaction without itself undergoing a permanent change.

Question 12

Which of the following statements about acids and bases is correct according to the Lowry-Brønsted theory?

Accepted Answer

An acid is a proton donor and a base is a proton acceptor.

Question 13

Which of the following is an example of a weak acid?

Accepted Answer

Ethanoic acid ($$\mathrm{CH_3COOH})$$

Question 14

A student is titrating $$25.0\ \mathrm{cm^3$} of$$ $$0.100\ \mathrm{mol\ dm$$^{-3}$$}$$ hydrochloric acid ($$\mathrm{HCl}) $$with sodium hydroxide ($$\mathrm{NaOH}). $$The balanced equation is $$\mathrm{HCl}(aq) + \mathrm{NaOH}(aq) \rightarrow \mathrm{NaCl}(aq) + \mathrm{H_2O}(l). If$$ $$20.0\ \mathrm{cm^3$} of$$ $$\mathrm{NaOH} is $$required to reach the equivalence point, what is the concentration of the $$\mathrm{NaOH}$$ solution?

Accepted Answer

$$C_1V_1 = C_2V_2 \Rightarrow (0.100 	imes 25.0) = (C_2$ 	imes 20.0) \Rightarrow C_2$ = 0.125\ \mathrm{mol\ dm$$^{-3}$$}$$

Question 15

Which of the following best describes an ampholyte, and which is a common example?

Accepted Answer

A substance that can act as both an acid and a base; water ($$\mathrm{H_2O}) is a $$common example.

Question 16

What is the pH of a $$0.01\ \mathrm{mol\ dm$$^{-3}$$}$$ solution of a strong acid such as $$\mathrm{HCl} at$$ $$25^\circ\mathrm{C}$$?

Accepted Answer

$$\mathrm{pH} = -\log[\mathrm{H_3O^+}] = -\log(0.01) = 2$$

Question 17

Which of the following best explains why strong acids conduct electricity better than weak acids at the same concentration?

Accepted Answer

Strong acids ionize completely in water, producing a higher concentration of ions.

Question 18

Which of the following is the correct expression for the ion product of water ($$K_w) at$$ $$25^\circ\mathrm{C}$$?

Accepted Answer

$$K_w = [\mathrm{H_3O^+}][\mathrm{OH^-}] = 1 	imes 10$$^{-14}$$

Question 19

A reaction mixture initially contains $$0.5\ \mathrm{mol\ dm$$^{-3}$$} of$$ $$\mathrm{A}$$ and $$0.5\ \mathrm{mol\ dm$$^{-3}$$} of$$ $$\mathrm{B}. $$After 10 seconds, the concentration of $$\mathrm{A}$$ decreases to $$0.3\ \mathrm{mol\ dm$$^{-3}$$}. $$What is the average rate of reaction with respect to $$\mathrm{A}$$ over this period?

Accepted Answer

$$	ext{Rate} = \dfrac{\Delta c}{t} = \dfrac{0.5 - 0.3}{10} = 0.02\ \mathrm{mol\ dm$$^{-3}$$\ s$$^{-1}$$}$$

Energy, Chemical Change, and Acid-Base Chemistry: Study Notes for Introductory Chemistry

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