Kinetics - Rates of Reactions

Rate = Change in concentration / TIME for change to occur

THe change in concentration can b measured by:

• Appearance of disappearace of colour
• Volume of gas evolved
• Changes in PH
• Heat produced
• Changes in pressure (reactions involving gases)

Rate Equation: is defined as the change in concentraton (of any reactants or products)with unit time

Order of Reaction: the power to which the concentrations of the reactants are raised to the rate equation

Rate = K[A] ^a [B] ^b

^{[ ] - stand for concentration}

^{K = a constant for a particular reaction at a given temperature - known as the rate constant.}

^{(any number raised to the power of 0 = 1)}

^{Faster reactions have larger K values}

^{A catalyst does not increase the K value - it causes a different reaction mechanism with a DIFFERENT K value}

^{The only factor that affects the value of K is temperature}

^{a + b - the orders. To get the overall order of the reaction, add all the powers together}

^{Zero Order}

^{If doubling the concentration of one reactant has no affect on the rate it is sadi to hav zero order w.r.t that reactant}

^Graph:

^{First Order:}

^{If doubling the [reactant] doubles the rate of the reaction then it is said to be forst order w.r.t [reactant] (i.e if bothe go up by the same number it is first order)}

^Graph:

^{Second Order:}

^{If doubling [reactant] increases the rate by 4 then the reaction is said to be second order.}

^Graph:

^{Measuring Rates of Reactions:}

^{Rate is measured in moldm-3s-1}

^{The seconds can also be either minutes or hours depending on the speed of the reaction.}

^{Rate decreases as time proceeds - the fewer collisions, the slower the rate of reaction}

^{Initial Rate: the rate at the start of the reaction}

^{Monitoring the rate can be:}

^{1. Continuous}

^or

^{2. For intial rate only}

^{Measuring Rates of Reactions:}

^{Rate is measured in moldm-3s-1}

^{The seconds can also be either minutes or hours depending on the speed of the reaction.}

^{Rate decreases as time proceeds - the fewer collisions, the slower the rate of reaction}

^{Initial Rate: the rate at the start of the reaction}

^{Monitoring the rate can be:}

^{1. Continuous}

^or

^{2. For intial rate only}