Q: A reaction is first order in $$\mathrm{N_2O_5}$$ and follows the rate law $$\text{rate} = k[\mathrm{N_2O_5}]. If $$the initial pressure of $$\mathrm{N_2O_5} is 312 $$torr and drops to 156 torr in 100 s, what is the value of the rate constant $$k (in$$ $$\mathrm{s$$^{-1}$$}$$)?

$$k = 6.93 \times 10$$^{-3}$$\ \mathrm{s$$^{-1}$$}$$

Q: For the reaction $$\mathrm{CH_4$(g) + 2 S_2$(g) \rightarrow CS_2$(g) + 2 H_2S(g)}$$, the rate constant at 550 $$^\circC is$$ $$1.1\ \mathrm{L\ $$mol^{-1}$$\ s$$^{-1}$$}$$ and at 625 $$^\circC is$$ $$6.4\ \mathrm{L\ $$mol^{-1}$$\ s$$^{-1}$$}. $$What is the activation energy $$E_a$$ for this reaction? ($$R = 8.314\ \mathrm{J\ $$mol^{-1}$$\ K$$^{-1}$$})$$

$$4.1 \times 10^4$\ \mathrm{J\ $$mol^{-1}$$}$$

Question 1

For the reaction $$\mathrm{H_2SeO_4(aq) + 6 I^-(aq) + 4 H^+(aq) ightarrow $$SeO_2$$(aq) + 2 I_2$(aq) + 3 H_2O(l)}$$, the rate law is determined to be $$	ext{rate} = k[\mathrm{H_2SeO_4}]^x[\mathrm{I^-}]^y[\mathrm{H^+}]^z. If $$doubling $$[\mathrm{I^-}]$$ while keeping other concentrations constant causes the rate to quadruple, what is the value of $$y$$?

Accepted Answer

$$y = 2$$

Question 2

A reaction is first order in $$\mathrm{N_2O_5}$$ and follows the rate law $$	ext{rate} = k[\mathrm{N_2O_5}]. If $$the initial pressure of $$\mathrm{N_2O_5} is 312 $$torr and drops to 156 torr in 100 s, what is the value of the rate constant $$k (in$$ $$\mathrm{s$$^{-1}$$}$$)?

Accepted Answer

$$k = 6.93 	imes 10$$^{-3}$$\ \mathrm{s$$^{-1}$$}$$

Question 3

The decomposition of $$\mathrm{N_2O_5} at 500 K is $$first order. If the initial pressure is 312 torr, what will the pressure be after 900 s? Use $$k = 6.93 	imes 10$$^{-3}$$\ \mathrm{s$$^{-1}$$}.$$

Accepted Answer

$$0.63$$ torr

Question 4

For the reaction $$\mathrm{CH_4$(g) + 2 S_2$(g) \rightarrow CS_2$(g) + 2 H_2S(g)}$$, the rate constant at 550 $$^\circC is$$ $$1.1\ \mathrm{L\ $$mol^{-1}$$\ s$$^{-1}$$}$$ and at 625 $$^\circC is$$ $$6.4\ \mathrm{L\ $$mol^{-1}$$\ s$$^{-1}$$}. $$What is the activation energy $$E_a$$ for this reaction? ($$R = 8.314\ \mathrm{J\ $$mol^{-1}$$\ K$$^{-1}$$})$$

Accepted Answer

$$4.1 	imes 10^4$\ \mathrm{J\ $$mol^{-1}$$}$$

Question 5

A catalyst lowers the activation energy of a reaction from $$4.1 	imes 10^4$\ \mathrm{J\ $$mol^{-1}$$} to$$ $$1.0 	imes 10^4$\ \mathrm{J\ $$mol^{-1}$$} at 550$$ $$^\circC. $$What is the ratio of the catalyzed to uncatalyzed rate constants at this temperature? ($$R = 8.314\ \mathrm{J\ $$mol^{-1}$$\ K$$^{-1}$$})$$

Accepted Answer

$$345$$

Question 6

For the reaction $$\mathrm{NO_2$(g) + O_3$(g) \rightarrow NO_3$(g) + O_2$(g)}$$, the rate triples when the temperature increases from 25 $$^\circC to 35$$ $$^\circC. $$What is the activation energy $$E_a$$ for the forward reaction? ($$R = 8.314\ \mathrm{J\ $$mol^{-1}$$\ K$$^{-1}$$})$$

Accepted Answer

$$84\ \mathrm{kJ\ $$mol^{-1}$$}$$

Question 7

Given $$\Delta E = 83\ \mathrm{kJ\ $$mol^{-1}$$}$$ for the reaction $$\mathrm{NO_2$(g) + O_3$(g) ightarrow NO_3$(g) + O_2$(g)}$$ and $$E_{a,	ext{fwd}} = 84\ \mathrm{kJ\ $$mol^{-1}$$}$$, what is the activation energy for the reverse reaction?

Accepted Answer

$$167\ \mathrm{kJ\ $$mol^{-1}$$}$$

Question 8

At equilibrium, the partial pressure of $$\mathrm{S_8$(g)} is$$ $$0.25$$ atm for the reaction $$\mathrm{S_8$(g) \rightleftharpoons 4 S_2$(g)} at$$ $$1325 K. $$What is the value of $$K_p at $$this temperature?

Accepted Answer

$$324$$

Question 9

For the reaction $$\mathrm{S_8$(g) \rightleftharpoons 4 S_2$(g)}$$, $$K_p at$$ $$1325 K is$$ $$324. $$What is the value of $$K_c at$$ $$1325 K$$? ($$R = 0.0821\ \mathrm{L\ atm\ $$mol^{-1}$$\ K$$^{-1}$$})$$

Accepted Answer

$$2.4 	imes 10$$^{-4}$$

Question 10

For the reaction $$\mathrm{NOCl(g) ightleftharpoons NO(g) + \frac{1}{2}Cl_2$(g)}$$, a mixture of $$1.0$$ mol $$\mathrm{NOCl}$$, $$1.0$$ mol $$\mathrm{NO}$$, and $$1.0$$ mol $$\mathrm{Cl_2$} is $$placed in a $$2.0 L $$flask at $$35^\circC. If$$ $$K_c = 1.6 	imes 10$$^{-5}$$, what is the equilibrium concentration of $$\mathrm{NOCl}$$?

Accepted Answer

$$0.996\ \mathrm{M}$$

Question 11

A reaction mixture initially contains $$1.0$$ mol $$\mathrm{NOCl}$$, $$1.0$$ mol $$\mathrm{NO}$$, and $$1.0$$ mol $$\mathrm{Cl_2$} in a$$ $$2.0 L $$flask at $$35^\circC. At $$equilibrium, what is the concentration of $$\mathrm{NO}$$? ($$K_c = 1.6 	imes 10$$^{-5}$$)

Accepted Answer

$$0.004\ \mathrm{M}$$

Question 12

For the decomposition of $$\mathrm{$$CCl_4$$(g) \rightarrow C(s) + 2Cl_2(g)} at$$ $$700^\circC$$, $$K_p = 0.76. If $$the total pressure at equilibrium is $$1.20$$ atm, what is the partial pressure of $$\mathrm{Cl_2$} at $$equilibrium?

Accepted Answer

$$0.876$$ atm

Question 13

For the reaction $$\mathrm{$$CCl_4$$(g) \rightarrow C(s) + 2Cl_2(g)} at$$ $$700^\circC$$, if the total pressure at equilibrium is $$1.20$$ atm, what was the initial pressure of $$\mathrm{$$CCl_4$$}$$ placed into the container?

Accepted Answer

$$0.552$$ atm

Question 14

A first-order reaction has a rate constant $$k = 6.93 	imes 10$$^{-3}$$\ \mathrm{s$$^{-1}$$}. $$What is the half-life of the reaction?

Accepted Answer

$$100 s$$

Question 15

For a reaction with $$\Delta H^\circ = 98.3\ \mathrm{kJ\ $$mol^{-1}$$}$$, $$K_p at$$ $$1325 K is$$ $$324. $$What is $$K_p at$$ $$298 K$$? ($$R = 8.314\ \mathrm{J\ $$mol^{-1}$$\ K$$^{-1}$$})$$

Accepted Answer

$$2.4 	imes 10$$^{-9}$$

Question 16

Which of the following best describes the effect of a catalyst on a chemical reaction?

Accepted Answer

It decreases the activation energy and increases the rate constant.

Question 17

If the rate law for a reaction is $$	ext{rate} = k[\mathrm{A}]^2[\mathrm{B}]$$, what is the overall order of the reaction?

Accepted Answer

Third order

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