Chemistry 30

Explain why the rate of a chemical reaction increases as the concentration of the reactants increases.

Consider two gases A and B in a container at room temperature. What effect will the following changes have on the reaction rate between these gases (increase, decrease, no effect)?

a. The pressure is increased.

b. The number of molecules of gas A is doubled

c. The temperature is decreased

a.   C₁₂H_{26 (s)} + 18.5 O_{2 (g)} → 12 CO_{2 (g)} + 13 H₂O_(g)

b.    S₂O₈^2-_(aq) + 2 I^–_(aq) → 2 SO₄^2-_(aq) + I_{2 (s)}

c.   Ba²⁺_(aq) + SO₄^2-_(aq) → BaSO_{4 (s)}

Hydrogen peroxide reacts with hydrogen ions and iodide ions according to the reaction mechanism shown below:

1. Determine the overall reaction described by this mechanism
2. If you wanted to increase the rate of the overall reaction, would it be better to increase the concentration of H⁺ or I^–. Why?

At 20°C, a small strip of magnesium reacts with 3.0 M hydrochloric acid to produce 12 mL of hydrogen gas in 20 s.

1. Calculate the rate of this reaction.
2. Predict the volume of hydrogen might be produced in 20 s at 30 ° C?

hint – what change in temperature has occurred? What is the general rule for what happens to the rate with this amount of temperature change? At this new rate, how many mL will be produced in 20 seconds?

Consider the following potential energy diagram:

1. Is the forward reaction endothermic or exothermic:
2. Determine ΔH for the forward reaction:
3. Determine ΔH for the reverse reaction:
4. Determine E_a for the forward reaction:
5. Determine E_a for the reverse reaction:
6. Label the location of the activation complex in the diagram.
7. Add to the diagram a possible pathway for a catalyzed reaction.

Sketch a potential energy curve for an reaction based on the information provided below.

Δ H_forward = -30 kJ      E_areverse = +50 kJ

Label the parts representing the activated complex, activation energy, and change in enthalpy, ΔH.