chapter 18 Flashcards
rate=
change in conc/ time
zero order
- conc of reactant has no effect on the rate
- rate= [A]0
- any number to power of zero is one
first order
- rate depends on conc of a reactant to a power of 1
- rate= [A]1
- if conc of a is doubled the rate increases by a factor of 2
- if conc of a is tripled the rate increases by a factor of 3
second order
- when the rate of a reaction depends on its conc raised to the power of 2
- rate= [A]2
- if conc of a is doubled, the rate increases by a factor of 2 squared= 4
the rate equation
rate= k [A]m [B}n (m & n)- orders of reaction
the rate constant
k, is the proportionality constant, it is the number that mathematically converts between the rate and conc of orders
overall order
=sum of orders with respect to each reactant
rate = k[A]m[B]n, m + n
shape of a zero order graph
-straight line with a negative gradient
-reaction rate does not change during the course of the reaction
gradient= k
shape of a first order graph (conc-time)
-downward curve, with a decreasing gradient over time
shape of a second order graph (conc-time)
-downward curve, but steeper at the start than 1st, and tailing off more slowly
half-life (conc-time)
- t1/2, the time taken for half of a reactant to be used up
- first order reactions have a constant half-life- conc halving every half-life- exponential decay
calculating rate constant from the half-life
k= ln2/ t1/2
shape of a zero order rate-conc graph
- horizontal straight-line, with a 0 gradient
- rate=k
- y intercept gives the rate constant k
- rate does not change with increasing conc
shape of a first order rate-conc graph
- straight-line graph through the origin
- rate= k[A]
- rate is directly proportional to conc
- k= gradient
shape of a second order rate-conc graph
- upward curve with an increasing gradient
- rate= k[A]2
