Review Sheet – Chemistry, Level 3 –Equilibrium & Kinetics

Name: ______Date:______Period:___

Test Expectations

The student should be able:

  • Use the basic vocabulary of equilibrium and reversible reactions.
  • Use the Law of Mass Action to develop the equilibrium expression for a reaction for both homogeneous and heterogeneous reactions.
  • Calculate a reaction quotient and use it determine the direction that a reaction will proceed.
  • Analyze the direction a reaction will proceed using Le Chatelier’s Principle.
  • Describe collision theory and how it relates to the factors that affect reaction rate.
  • Draw an energy diagram that shows activation energy, overall enthalpy, reaction pathway, the activated complex, transition state/intermediate, and the effects of a catalyst or inhibitor
  1. Define each of the following terms clearly and completely.

(a)chemical equilibrium –

(b)reversible reaction–

(c)equilibrium constant –

(d)reaction quotient –

(e)Le Chatelier’s Principle –

(f)Homogeneous/heterogeneous equilibria –

(g)chemical kinetics –

(h)collision theory –

(i)effective/ineffective collisions –

(j)activation energy –

(k)activated complex (transition state) –

(l)reaction pathway –

  1. Write the equilibrium expressions for the following reactions:
  1. 2 CO(g)  C(s) + CO2(g)

B. 4 HCl(g) + O2(g)  2 H2O(g) + 2 Cl2(g)

  1. What is the reaction quotient (Q) for NH4Cl(s)  NH3(g) + HCl(g) given the following concentrations: [NH3] = .6 M, [HCl] = .2 M?
  1. For the reaction H2(g) + I2(g)  2 HI(g), the following concentrations are measured at a particular time: [H2] = 0.2 M, [I2} = 0.15 M, [HI] = 0.8 M. The Keq for this reaction is 50.5. Has this reaction reached equilibrium? If not, in which direction will the reaction proceed?

Q < Keq, so this reaction is not at equilibrium. There are too many reactants, so PRODUCTS will be made.

  1. You have the reaction:(Le Chatelier Question!)

N2(g) + 3 H2(g)  2 NH3(g) + heat

Describe what happens to the concentrations of each if the changes below are made.

a.The pressure is increased.

If the pressure is increased, the side with fewer gas products will be favored. That side is the products (2 particles of gas vs. 4 particles on the reactant side). Keq will not change.

b.The concentration of H2 is increased.

If the concentration of H2, a reactant, is increased then the reaction will shift to counteract this change. This shift will be away from reactants and towards more products.

c.The temperature is increased.

If the temperature is increased, the endothermic reaction will be favored. Since this reaction produces heat, it is exothermic, so the reverse reaction will be favored and more reactants will be made. Since products are consumed and reactants are made, the Keq will decrease.

  1. At 100°C, Kc = 0.078 for the following reaction:

SO2Cl2(g) SO2(g) + Cl2(g)

In an equilibrium mixture of the three gases, the concentrations of SO2Cl2 and SO2 are 0.136 M and 0.072 M, respectively. What is the [Cl2] in the equilibrium mixture?

7. State the effect that each of the following changes would have on the rate of a reaction.

  1. Decreasing the volume of a reaction in the gas phase.

Decreasing the volume packs the particles closer together so that they collide more frequently. More frequent collisions leads to a FASTER reaction according to Collision Theory.

  1. Using small pieces of solid reactant rather than one large piece of the same mass.

Using small pieces raises the surface area of the reactant. A higher surface area leads to more collisions and more collisions gives a FASTER reaction.

  1. Lowering the temperature of the reactants.

Lowering the temperature will reduce the number of collisions and also lower the energy of these collisions. Both of these will make the reaction SLOWER.

  1. Adding more water to a reaction in solution.

Adding more water to a reaction will dilute the solution (lower the concentration). Lower concentration results in fewer collisions and therefore a SLOWER reaction rate.

  1. Adding a catalyst.

Adding a catalyst lowers the activation energy of the reaction (see # 9) and therefore results in a FASTER reaction rate.

8. Consider the hypothetical reaction:

A(g) + B(g)  C(g) ΔH = + 34 kJ

  1. Draw a potential energy versus reaction coordinate for the reaction. Label the energy of the reactants and products, the energy of the activated complex, and all significant energy differences.
  2. On the same diagram indicate the change or changes that result from the addition of a catalyst. Explain the role of the catalyst in changing the rate of the reaction.

This is an endothermic reaction (H is positive). See the class notes (Powerpoint) or textbook for sample diagrams.