## 7A.7bc

$\frac{d[R]}{dt}=-k[R]; \ln [R]=-kt + \ln [R]_{0}; t_{\frac{1}{2}}=\frac{0.693}{k}$

KDang_1D
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### 7A.7bc

7A.7 Express the units for rate constants when the concentrations are in moles per liter and time is in seconds for (a) zeroth-order reactions; (b) first-order reactions; (c) second-order reactions.

Why do you divide by mol/L for first and second order reactions?

Diana A 2L
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### Re: 7A.7bc

KDang_1D wrote:
7A.7 Express the units for rate constants when the concentrations are in moles per liter and time is in seconds for (a) zeroth-order reactions; (b) first-order reactions; (c) second-order reactions.

Why do you divide by mol/L for first and second order reactions?

The rate of a reaction is usually given as mol L^-1 s^-1 (concentration per unit of time). For first order reactions, the concentration of one reactant takes care of the unit for concentration, so the rate constant is given in units of s^-1. For second order reactions, there are two units of concentration already present, so the rate will be s^-1 divided by concentration unit. Hope that helps:)

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