Rate of Reactions

Question

Kinetics is the study of how the amount (concentration) of any one of the reactants or products changes with time. When pieces of a metal (M) were placed in solutions of hydrochloric acid, the following reaction occurred:

M _(s) + 2H⁺ _(aq)  ↔ M²⁺ _(aq) + H_{2 (g)}

The times required for complete reaction of 0.010 grams of metal are listed in the table.

Acid concentration, M	Reaction time in seconds
0.25	189
0.50	85
1.50	29
3.00	14

Calculate the reaction rate in g/sec for 0.25 M HCl.

Answer 1

You need to determine the reaction is 1st order or 2nd order by using the data to convert the molar concentration to Ln [HCl] and 1/ [HCl] by using the TI calculator. You also can use TI calculator to graph Ln [HCl] vs.time and 1/ [HCl] vs time to see which one is more linear?

For Ln [HCl], the regression value (r) = -0.94

For 1/ [HCl], the regression value (r) = 0.999 therefore the reaction is 2nd order and the linear equation is

y = 0.021x + 0.89. the k = 0.021

The rate law is: Rate = .0.021 [HCl]² when the concentration is 0.25, the rate = 0.021 x (0.25)² = 0.0013 M/s

0.0013 mol/L x 36.5 g/mol = 0.048 g/L So the rate = 0.048 g/L-s