Review Problems

Water can be made from hydrogen and oxygen:H2 (g) + O2 (g) → H2O (g) Some experiments are run in a sealed 1 L flask at 350 K to

determine the initial rate of reaction for different concentrations of reactants:

[H2 ] M [O2] M Rate of formation of H2O M/sec

0.050 0.100 0.00480.050 0.050 0.00250.100 0.025 0.00120If I began with 0.050 moles of both reactants, how long

would it take to make 0.01 moles of water?

Orders of reaction

[H2 ] M [O2] M Rate of formation of H2O M/sec

0.050 0.100 0.00480.050 0.050 0.00250.100 0.025 0.00120Rate = k[H2]x[O2]y

Rate 1 = k[0.050]x[0.100]y

Rate 2 = k[0.050]x[0.050]y

0.0048 = [0.100]y

0.0025 = [0.050]y

1.92 =2y

Y =1

Orders of reaction[H2 ] M [O2] M Rate of formation of H2O M/sec0.050 0.100 0.00480.050 0.050 0.00250.100 0.025 0.00120Rate = k[H2]x[O2]y

Rate 2 = k[0.050]x[0.050]

Rate 3 = k[0.100]x[0.025]0.0025 = [0.100]x 2

0.0012 = [0.050]x

2.08 =2*2x

1.04 =2x

X=0

Rate = k[O2]

[H2 ] M [O2] M Rate of H2O M/sec0.050 0.100 0.00480.050 0.050 0.00250.100 0.025 0.001200.0048 M/s = k [0.100 M]K =0.048 s-1

0.0025 = k [0.050]K =0.05 s-1

0.0012 =k[0.025]K =0.048 s-1

Kavg = 0.0487 s-1

1st order kinetics

ln [O2]t= - kt

[O2]0

2H2 (g) + O2 (g) → 2H2O (g)

If I began with 0.050 moles of both reactants, how long would it take to make 0.01 moles of water?

0.010 mol H2O * 1 mol O2 = 0.005 mol O2

2 mol H2O

0.050 mol O2 started – 0.005 mol O2 reacted = 0.045 mol left

1st order kinetics

ln [O2]t= - kt

[O2]0

Ln (0.045/0.05) = - 0.0487s-1 tt = 2.16 seconds!