Q: Given the reaction $$2Cr(OH)_3 (s) + 2NaClO_3 (aq) + 3H_2O_2 (aq) \rightarrow 2Na^+ (aq) + 2CrO_4$$^{2-}$$ (aq) + 2Cl^- (aq) + 8H_2O (l)$$ with $$\Delta H_{rxn} = -240.2\ \mathrm{kJ}$$, what is the enthalpy change when 1.00 kg of $$Cr(OH)_3$$ reacts completely? (Molar mass $$Cr(OH)_3 = 99.99\ \mathrm{g/mol})$$

$$-1.20 \times 10^3$\ \mathrm{kJ}$$

Question 1

Which of the following is the correct balanced equation for the standard enthalpy of formation of sodium acetate trihydrate, $$\mathrm{NaC_2H_3O_2 \cdot 3H_2O (s)}$$?

Accepted Answer

$$\mathrm{Na (s) + 2C (s) + 2H_2 (g) + 2O_2 (g) + 3H_2O (l) \rightarrow NaC_2H_3O_2 \cdot 3H_2O (s)}$$

Question 2

Given the reaction $$2Cr(OH)_3 (s) + 2NaClO_3 (aq) + 3H_2O_2 (aq) \rightarrow 2Na^+ (aq) + 2CrO_4$$^{2-}$$ (aq) + 2Cl^- (aq) + 8H_2O (l)$$ with $$\Delta H_{rxn} = -240.2\ \mathrm{kJ}$$, what is the enthalpy change when 1.00 kg of $$Cr(OH)_3$$ reacts completely? (Molar mass $$Cr(OH)_3 = 99.99\ \mathrm{g/mol})$$

Accepted Answer

$$-1.20 	imes 10^3$\ \mathrm{kJ}$$

Question 3

A mixture of $$He(g)$$ and $$Ne(g)$$ has a total pressure of $$1.00\ \mathrm{atm} at$$ $$50.0\ \mathrm{L}$$ and $$0.40\ \mathrm{mol} of$$ $$He$$ and $$0.25\ \mathrm{mol} of$$ $$Ne. $$What is the partial pressure of $$He in $$the mixture?

Accepted Answer

$$0.62\ \mathrm{atm}$$

Question 4

The reaction $$CH_3COCH_3(aq) + HOCl(aq) \rightarrow CH_3COCH_2Cl(aq) + H_2O(l) is $$catalyzed by $$OH^-$$ and is first order in $$[CH_3COCH_3]$$, first order in $$[OH^-]$$, and zero order in $$[HOCl]. If $$the initial concentrations of $$CH_3COCH_3$$ and $$HOCl$$ are increased by a factor of 2.5 and $$[OH^-]$$ remains unchanged, by what factor does the rate increase?

Accepted Answer

2.5

Question 5

The following reaction is first order in $$[N_2O_5]$$ and its rate constant is $$3.46 	imes 10$$^{-5}$$\ \mathrm{s}^{-1} at$$ $$20^\circ C$$: $$2N_2O_5 (g) ightarrow 4NO_2 (g) + O_2$ (g). $$What time in minutes would it take for the reaction to consume 99% of the initial amount of $$N_2O_5$$?

Accepted Answer

$$2.22 	imes 10^3$ min

Question 6

For the reaction $$A \rightarrow C$$ via two steps: $$A \rightarrow B ($$slow), $$B \rightarrow C ($$fast), which of the following statements is correct?

Accepted Answer

The rate-determining step is $$A \rightarrow B.$$

Question 7

Consider the reversible reaction: $$HSO_4^- (aq) + H_2O (l$$) \rightleftharpoons $$SO_4$$^{2-} (aq) + H_3O^+ (aq)$$ with $$\Delta H_{rxn} \u003e 0$$. If the temperature is increased, in which direction will the equilibrium shift?

Accepted Answer

Right

Question 8

Which of the following is the correct expression for the equilibrium constant $$K$$ for the reaction $$HSO_4^- (aq) + H_2O (l$$) \rightleftharpoons $$SO_4$$^{2-} (aq) + H_3O^+ (aq)$$?

Accepted Answer

$$K = \dfrac{[SO_4$^{2-}][H_3O^+]}{[$$HSO_4$$^-]}$$

Question 9

Which of the following pairs is a correct conjugate acid-base pair for the reaction $$HSO_4^- (aq) + H_2O (l$$) \rightarrow $$SO_4$$^{2-} (aq) + H_3O^+ (aq)$$?

Accepted Answer

$$HSO_4$$^-$$ / SO_4$^{2-}$$

Question 10

Rank the following in order of increasing acid strength: $$H_2SO_4$$, $$HNO_3$$, $$HClO_4.$$

Accepted Answer

$$HNO_3$$ \u003c H_2SO_4 \u003c $$HClO_4$$

Question 11

Which of the following solutions has the lowest pH?

Accepted Answer

$$0.010\ \mathrm{M}\ HCl$$

Question 12

Calculate the pH of a $$0.050\ \mathrm{M}\ HBr(aq)$$ solution. ($$pK_a(HBr) = -9 at$$ $$25^\circ C)$$

Accepted Answer

1.30

Question 13

Which of the following statements about the effect of a catalyst on a reaction is correct?

Accepted Answer

A catalyst lowers the activation energy, increasing the reaction rate.

Question 14

Which of the following salts will produce a basic solution when dissolved in water?

Accepted Answer

$$Na_2CO_3$$

Question 15

Which of the following has the highest entropy of vaporization?

Accepted Answer

$$CH_3OH$$

Question 16

Which of the following is the strongest acid?

Accepted Answer

$$HClO_4$$

Question 17

Which of the following is the correct rate law for a reaction that is first order in $$A$$ and second order in $$B$$?

Accepted Answer

$$rate = k[A][B]^2$$

Question 18

Which of the following will increase the rate of a chemical reaction?

Accepted Answer

Increasing the temperature

Question 19

Which of the following is the correct expression for the Arrhenius equation?

Accepted Answer

$$k = A e$$^{-E_a/(RT)}$$

General Chemistry Exam 3 Study Guide: Thermochemistry, Chemical Kinetics, Equilibrium, and Acids/Bases

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