For the reaction :2A + B → A2Bthe rate = k[A][B]2 with k = 2.0 ×

1.	For the reaction :2A + B → A2Bthe rate = k[A][B]2 with k = 2.0 × 10-6 mol-2 L2 s-1.Calculate the initial rate of the reaction when [A] = 0.1 mol L-1 [B] = 0.2 mol L-1.Calculate the rate of reaction after [A] is reduced to 0.06 mol L-1.
Answer» Initial rate = k[A][B]² But [A] = 0.1 M, [B] = 0.2 M and k = 2.0 × 10^-6 mol^-2 L² s^-1 ∴ Initial rate = 2.0 × 10^-6 mol^-2 L² s^-1 × 0.1 M × (0.2 M)² = 8 × 10^-9 M s^-1 From the equation 2A + B → A₂B it is clear that when 2 moles of A are used then 1 mol of B is used in the same time. Therefore, when A has been reduced to 0.06 M , 0.04 M of A and hence 0.02 M of B have reacted. Thus, Concentration of A left = [A] = 0.06 M Concentration of B left = [B] = (0.2 M – 0.02 M) = 0.18 M Rate = k[A][B]² = 2.0 × 10^-6 mol^-2 L² s^-1 × 0.06 M × (0.18 M)² = 3.89 × 10^-9 M s^-1

For the reaction :2A + B → A2Bthe rate = k[A][B]2 with k = 2.0 × 10-6 mol-2 L2 s-1.Calculate the initial rate of the reaction when [A] = 0.1 mol L-1 [B] = 0.2 mol L-1.Calculate the rate of reaction after [A] is reduced to 0.06 mol L-1.

Answer»

Initial rate = k[A][B]²

But [A] = 0.1 M, [B] = 0.2 M and

k = 2.0 × 10^-6 mol^-2 L² s^-1

∴ Initial rate

= 2.0 × 10^-6 mol^-2 L² s^-1 × 0.1 M × (0.2 M)²

= 8 × 10^-9 M s^-1

From the equation 2A + B → A₂B it is clear that when 2 moles of A are used then 1 mol of B is used in the same time. Therefore, when A has been reduced to 0.06 M , 0.04 M of A and hence 0.02 M of B have reacted.

Thus,

Concentration of A left = [A] = 0.06 M

Concentration of B left = [B] = (0.2 M – 0.02 M) = 0.18 M

Rate = k[A][B]²

= 2.0 × 10^-6 mol^-2 L² s^-1 × 0.06 M × (0.18 M)²

= 3.89 × 10^-9 M s^-1

Discussion

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