Initial rates and the rate constant 122-123

Question 1

2NO(g) + O₂(g) → 2NO₂(g)

Three experiments are carried out to investigate the rate of this reaction. After the first experiment, the concentration of each reactants is varied.

Determine the orders, use the orders to write the rate equation and then find the value of rate constant,k.

Answer 1

Comparing experiments 1 and 2:

• [NO] has been kept constant.
• [O₂] has increased by 3 times; the rate has also increased by 3 times.
• So the order with respect to O₂ = 1.

Comparing experiments 1 and 3:

• [O₂] has been kept constant.
• [NO] has increased by 2 times; the rate has increased

by 4 = 2² times.

• So the order with respect to NO = 2.

Calcuate the rate constant:

k = rate/([NO]²[O₂])

K is calculated using values from one of the experiments.

K = 1820 dm⁶mol^-2s^-1

Question 2

Explain why the rate of reaction inreases with temperature in terms of k.

Answer 2

• The larger the value of k, the faster the reaction.
• Raising the temperature speeds up the rate of most reactions by increasing the rate constant, k.
• For many reactions, the rate doubles for each 10*C increase in temperature. This reflects the greater number of reacting particles that exceed the activation energy.