COTW10

The diagram represents the Maxwell-Boltzmann energy distribution curve of the reactants for a chemical reaction with different activation energies, E_a1 and E_a2.
What is the reason why the rate of the reaction with activation energy E_a2 is greater?

• More frequent collisions between the particles occur.
• More energetic collisions between the particles occur.
• A catalyst has been added.
• The temperature is higher.

X and Y react according to the equation 2X + Y --> Z.  The reaction can be described by the following mechanism:
X + X --> X₂  slow
X₂ + Y --> Z  fast
What is the order of the reaction with respect to X and Y?

• X is first order; Y is zero order
• X is first order; Y is first order
• X is second order; Y is zero order
• X is second order; Y is first order

The rate constant for a reaction is determined at different temperatures.  Which diagram represents the relationship between the rate constant, k, and temperature, T, in K?

• A
• B
• C
• D

Which statement is correct for the reversible reaction when K_c >> 1?

• The reaction almost goes to completion.
• The reaction hardly occurs.
• Equilibrium is reaches in a very short time.
• At equilibrium, the rate of the forward reaciton is much higher than the rate of the backward reaction.

The diagram represents the vapour pressure of two liquids, A and B, as temperature changes.  Y is a point on the curve of liquid A.  Which statement can be made using the graph?

• At the conditions of pressure and temperature at point Y, A is in the liquid phase and B is in the gaseous phase.
• At the conditions of pressure and temperature at point Y, both A and B are in the gaseous phase.
• At the same pressure, A has a higher boiling point than B.
• The intermolecular forces between the molecules of B are stronger than between the molecules of A.

THIS IS A FREE RESPONSE, NOT MULTIPLE CHOICE! So answer all the questions.

Sodium thiosulfate solution, Na₂S₂O₃(aq), and hydrochloric acid, HCl(aq), react to produce solid sulfur as in the equation below.

S₂O₃^2-(aq) + 2H⁺(aq) --> S(s) + SO₂(aq) + H₂O(l)

a) The data table shows the results used to determine the initial rate. Deduce, with a reason, the order of reaction with respect to each reactant.

b) State the rate expression for this reaction.

c) Determine the value of the rate constant, k, and state its units.

d) State an equation for a possible rate determining step for the reaction.

e) Suggest how the activation energy, E_a, for this reaction may be determined.

• I have answered ALL questions a-e.

• I did NOT answer all questions a-e.