11A.3 Flashcards
what are the two methods used to determine orders of reaction
- continuous method
2. initial rate method
what is the continuous method
it is to make a reaction mixture then take samples out of it, then stop the reaction in the sample possibly by quenching find the concentration on the reactant (by appropriate experimental method) then draw a concentration-time graph, then find the half-life of the reaction at different concentration, depending on the half-life you’ll find out the order of the reactant
if the half-life has a constant value in the concentration-time graph that tells us that the order is
the reactant is first order
if the half-life doubles as the reaction proceeds in a concentration-time graph that tells us that the order is
the reactant is second order
if the line in the concentration-time graph is constant with a negative gradient it tells us that
the reaction is constant no matter the concentration of the reactant, and the reactant is zero order
how do you calculate the rate from the concentration-time graph
you draw a tangent at a particular time find the x and y the use rate = - change in concentration/time
what is half life
it is the time taken for the concentration of a reactant to fall to one-half of its value
what is the instantaneous reaction rate
the gradient of a tangent to a line in a concentration-time graph, it carries as the reaction goes but not for zero order
what is the initial rate method
serval reaction mixuters are made up and teh intial rate (time take for a fixed amount of a product is being formed or a fixed amount of reactant being used) then we can calculte the mathematical reation between the rate of a reaction and the concentration of the reactant
why isn’t the initial rate of the product/reactant accurate
the initial rate assumes that the rate is constant for the whole time period ( since rate = 1/t)which isn’t true so the initial rate is actually the mean average rate over time and not the true rate over time, but the approximation is good enough to determine the order
since the amount of the product/reactant is kept the same we can say that the rat is
proportional to 1/t
how can we determine the order of a reactant using a 1/t x the concentration of a reactant graph
page 13
if plotting a 1/t x the concentration of a reactant graph what is necessary to do to check if its second order
polt a 1/t x the concentration of a (reactant)^2 graph and if its a straight line through the origin its second order
