# Lecture 26: Addition Reactions and Chemical Kinetics

• Takes place on a double bond
• Electrophile to C﻿$=$﻿C

### Chemical Kinetics

Reaction Rates - Measure how quickly they proceed in a given time. The speed of a chemical reaction is usually reported as its change in concentration (molarity) over time, molarity per second (M/s)

Average rate of appearance of ﻿$B = \frac{change \ in \ [B] }{change \ in \ time} = \frac{\Delta [B]}{\Delta t}$﻿

Average Rate of Disappearance of ﻿$A = \frac{change \ in \ [B]}{change \ in \ time} = - \frac{\Delta[A]}{\Delta t}$﻿

• Decreases and converts to ﻿$B$﻿

Relative Reaction Rate Equations - ﻿$\frac {\Delta B}{\Delta t}, \ \frac {\Delta [A]}{\Delta t}$﻿

﻿$*$﻿Rate of reaction decreases as the reaction proceeds because as the reaction proceeds, the amount of reactants decreases.

Overall Equation - For reaction: ﻿$2HI_{(g)} \rightarrow H_{2(g)} + I _ {2(g)}$﻿

﻿$- \frac{1}{2} \frac{\Delta [HI]}{\Delta t} = \frac {\Delta [H_2]}{\Delta t }= \frac {\Delta [I_2]}{\Delta t}$﻿

﻿$aA + bB \rightarrow cC + dD$﻿

﻿$- \frac{1}{a} \frac{\Delta [A]}{\Delta t} = - \frac{1}{b} \frac {\Delta [B]} {\Delta t}$﻿﻿$= \frac{1}{c} \frac{\Delta [C]}{\Delta t} = \frac{1}{d} \frac {\Delta [D]} {\Delta t}$﻿

Relationship between the rate and specific concentration is presented by the reaction order of a particular substance.

If doubling the concentration of one reactant ﻿$\Rightarrow$﻿ Rate doubles

﻿$=$﻿ First order Reaction

If doubling the concentration and the rate quadruples

﻿$=$﻿ Reaction is Second Order

If it doesn't effect the rate, it is ﻿$=$﻿ zero order

The overall Reaction order is the sum of the orders from the individual reactants ﻿$=$﻿ if a reaction is first order with respect to each reaction it is overall second order

#### Rate Law

﻿$aA + bB + cC \rightarrow dD + eE$﻿

rate ﻿$= K[A]^m [B]^n [C]^p$﻿

﻿$m=$﻿ order with respect to ﻿$A$﻿ ﻿$( m \neq a)$﻿

Not the coefficient from the equation. ﻿$m$﻿ is expressed

#### Experimentally,

Initial Rates Data - Experimental technique to find ﻿$m/n/p$﻿ by changing the initial concentrations of one reactant at a time then we can see the effect of one reactants concentration on the rate.

﻿$K =$﻿ rate ﻿$\cdot$﻿ constant (units)

First Order - ﻿$1/s$﻿

Second Order - ﻿$1/(s \cdot m)$﻿

ZERO Order - ﻿$m/s$﻿