5.1 Rates Equilibrium And pH

-is the change in concentration of a reactant or product per unit time

ORDER

-the rate constant (k) -is the constant that links the rate of reaction with the concentration of the reactants raised to the powers of their orders in the rate equation

-the rate equation for a reaction A+B—> C is given by : Rate=k[A]^m [B]^n -where m is the order of reaction with respect to A and n is the order of reaction with respect to B

-the sum of the individual orders -m+n

Rate of reaction(moldm^-3s^-1). = change in concentration of reactant or product ————————————————————————— Time

-if the order is 0 with respect to reactant A ,then: rate ∝[A]^0 -the rate is unaffected by changing the concentration of A -remember any number to the power of 0 is equal to 1

-proportional

-if the order is 1 with respect to a reactant A, then: rate ∝ [A]^1 -the rate is DIRECTLY PROPORTIONAL to the concentration ->if [A] increases by 2 times the rate also increases by 2 times -> if [A] increases by 3 times the rate also increases by 3 times

-if the order is 2 with respect to a reactant A then : rate ∝[A]^2 -the change in rate will be equal to the change in concentration squared ->if [A] increases by 2 times the rate increases by 2^2=4 times ->if [A] increases by 3 times the rate increases by 3^2=9 times

Rate=k[A]^x[B]^y[C]^z -k=rate constant -A-concentration of reactant A -B-concentration of reactant B -C-concentration of reactant C -x,y,z-orders of reaction for each reactant

-the half-life of a reactant is the time taken for the concentration of the reactant to reduce by half

-zero order -changes in concentration of this reactant have no effect on the rate -this is shown on a rate-concentration graph as a horizontal line - rate ∝ [A]^0

-first order -the concentration of the reactant and rate are directly proportional -doubling the concentration doubles the rate -this graph shows that rate ∝ [B]^1

-second order -the rate is proportional to the concentration of the reactant squared -if the concentration of the reactant is tripled the rate will be increased by 3^2 -the graph shows that the rate ∝ [C]^2

-calculate the gradient -gradient= change in y / change in x

-positive indices -alphabetically

-for reactions involving acids or bases, you can measure- .pH changes by carrying out titrations .pH changes by using a pH meter -for reactions that produce gases, you can measure- .the change in volume or pressure .the loss in mass of reactants -for reactions that produce visual changes (usually monitored by using a colorimeter) you can observe- .the formation of a precipitate .a colour change

-Colorimetry can be used to determine the rate of reaction for a reaction that involves the formation or depletion of a coloured species. -A colorimeter is a device that measures the amount of light that is absorbed by a solution. -The amount of light absorbed by the solution is proportional to the concentration of the coloured species. -In a colorimetry experiment, a calibration curve is often generated. -This involves using a colorimeter to measure the absorbance of solutions of known concentrations, from which a calibration curve is plotted. -Then, throughout the experiment, the absorbance of samples from the reaction mixture can be measured and the calibration curve used to convert the absorbance readings into concentration values. A concentration-time graph can then be plotted.

-continuous -continuous

-because first order reactions have constant half-lives , the value of the half-life can be used to calculate the rate constant

-the slowest step in the reaction mechanism of a multi-step reaction

The reaction mechanism must be worked out by looking at the rate equation and ensuring that : -a rate-determining step is given that involves the number of molecules shown by the order for that reactant (e.g if it is a second order there will be 2 molecules of that reactant) -subsequent steps are shown that eventually generate the products shown in the balanced equation -any intermediate generated is used up in the subsequent steps -the species involved in the reaction mechanism cancel out to leave the overall equation

-increase of temperature gives more energy to the molecules -means more frequent collisions that exceed the activation energy (more successful collisions) -raising the temperature speeds up the rate of most reactions by increasing the rate constant