Unit 1 Test 1

PrePublic Review #1

1.

Which is a single step reaction in a reaction mechanism? (A) activated complex (B) catalyst (C) elementary process (D) reaction intermediate

Name:_________________

2.

What happens when a catalyst is added to a reaction? (A) equilibrium constant changes (B) heat of reaction increases (C) new mechanism becomes available (D) rate of reaction decreases

Consider the potential energy diagram below for the next two questions.

3. Which describes the forward reaction? ΔH (kJ)

Reaction Type

(A) (B) (C) (D)

- 50 - 50 +50 +50

endothermic exothermic endothermic exothermic

5.

What is the catalyst in the mechanism below?

4. Which represents the activation energy for the reverse reaction? (A) A (B) B (C) C (D) D

H2O2 (aq) + I– (aq) → OI– (aq) + H2O (l) H2O2 (aq) + OI– (aq) → H2O (l) + I– (aq) + O2(g) (A) (B) (C) (D)

H2O2 I– OI– O2

6. Which graph best corresponds to the mechanism below, if the overall reaction is exothermic? Step 1

2 NO(g) + 2 H2(g) → N2(g) + 2 H2O(g)

Fast

Step 2

N2O2(g) → 2 NO(g)

Slow

Step 3

N2(g) + H2O(g) → N2O(g) + H2(g)

Fast

7. Which theory is based on the concept that all matter consists of particles in constant motion? (A) Arrhenius (B) Bohr (C) collision (D) kinetic molecular

9. What increases the rate of a chemical reaction without being consumed? (A) activated complex (B) catalyst (C) reactant (D) reaction intermediate

8. Which factor explains why potassium usually reacts faster than sodium? (A) concentration (B) nature of reactants (C) surface area (D) temperature

10. Which increases the reaction rate? (A) decreasing the frequency of collisions (B) decreasing ΔH for the reaction (C) increasing the frequency of collisions (D) increasing ΔH for the reaction

Use this potential energy diagram to answer the next two questions.

11. What is the activation energy for the forward reaction? (A) 100 kJ (B) 300 kJ (C) 600 kJ (D) 700 kJ

12. What is the heat of reaction for the reverse reaction? (A) -600 kJ (B) -200 kJ (C) 200 kJ (D) 600 kJ

13. What does X represent in the diagram to the right? (A) activation energy for the forward reaction (B) activation energy for the reverse reaction (C) heat of reaction for the forward reaction (D) heat of reaction for the reverse reaction

14. Which observation best supports the Kinetic Molecular Theory? (A) Acetic acid odour is detected from across the room. (B) Liquid water freezes at 0°C under standard conditions. (C) Nitrogen dioxide gas is dark brown in colour. (D) When burned, butane produces more heat per mole than propane. 15. What is the high energy, unstable chemical species that exists in the transition from reactants to products? (A) activated complex (B) catalyst (C) inhibitor (D) reaction intermediate

16. Calculate ΔH for the forward reaction if its activation energy is 20.0 kJ and the activation energy of the reverse reaction is 30.0 kJ? (A) -50.0 kJ (B) -10.0 kJ (C) 10.0 kJ (D) 50.0 kJ

17. What affect would increasing the surface area of a solid reactant have on a system approaching equilibrium? (A) decreases the rate of the forward reaction (B) decreases the time to reach equilibrium (C) increases the equilibrium concentration of products (D) increases the equilibrium concentration of reactants 18. For the reaction mechanism below, increasing the concentration of which species would have the greatest effect on the overall reaction rate? X+Y→2Z

slow

Z+2W→U

fast

Z+U→V

fast

(A) U (B) V (C) Y (D) Z 19. The table below describes two different reactions in which Reaction 1 is faster. What accounts for this observation? Reactants Temperature Concentration

Reaction 1 Fe2+(aq) + MnO4-(aq) 20 ⁰C 0.5 mol/L solution

Reaction 2 MnO4-(aq) + H2C2O4(aq) 40 ⁰C 1.0 mol/L solution

(A) nature of reactants (B) solution concentration (C) surface area (D) temperature 20. How does a catalyst speed up a chemical reaction? (A) doubles the concentration of reactants (B) increases the frequency of collisions (C) lowers the heat of reaction (D) provides an alternate pathway

Extended Response 21. For faster relief, should antacid medication should be chewed rather than swallowed whole? Explain.

22. Use the table below to answer the following questions. Reaction Mechanism

Rate of Reaction

Sign of ΔH

Step 1

OCl-(aq) + H2O(l) → HOCl(aq) + OH-(aq)

fast

negative

Step 2

HOCl(aq) + I-(aq) → HOI(aq) + Cl-(aq)

slow

positive

Step 3

HOI(aq) + OH-(aq) → H2O(l) + OI-(aq)

very fast

negative

(a) Write the equation for the overall reaction.

(b) Identify any reaction intermediates and/or catalysts present. Reaction Intermediate(s): Catalyst(s): (c)

Using the information from the table, and given that the overall reaction is exothermic, draw one possible potential energy diagram for the reaction.

23. 1.00 g of NaHCO3(s) reacted with different concentrations of CH3COOH(aq) at 25.0 ⁰C. The CO2(g) produced was collected in a 28.0 mL test tube. The table below shows the data collected in four trials. CH3COOH(aq) + NaHCO3(s) → NaCH3COO(aq) + CO2(g) + H2O(l) Trial 1 2 3 4

[CH3COOH(aq)] (mol/L) 1.0 0.83 0.67 0.5

time to fill tube(seconds) 11 19 32 47

(a) Calculate the rate of reaction for trial 2 and 3 in mL CO2(g) per s.

(b) Using collision theory, explain the difference in the rates of reaction for trial 2 and 3.

(c) The experimenter used NaHCO3(s) tablets for all trials. If the tablets were broken into pieces, estimate the rate of reaction for trial 3. Justify your answer.