chapter 18

Question 1

rate=

Answer 1

change in conc/ time

Question 2

zero order

Answer 2

• conc of reactant has no effect on the rate
• rate= [A]0
• any number to power of zero is one

Question 3

first order

Answer 3

• 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

Question 4

second order

Answer 4

• 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

Question 5

the rate equation

Answer 5

rate= k [A]m [B}n (m & n)- orders of reaction

Question 6

the rate constant

Answer 6

k, is the proportionality constant, it is the number that mathematically converts between the rate and conc of orders

Question 7

overall order

Answer 7

=sum of orders with respect to each reactant

rate = k[A]m[B]n, m + n

Question 8

shape of a zero order graph

Answer 8

-straight line with a negative gradient
-reaction rate does not change during the course of the reaction
gradient= k

Question 9

shape of a first order graph (conc-time)

Answer 9

-downward curve, with a decreasing gradient over time

Question 10

shape of a second order graph (conc-time)

Answer 10

-downward curve, but steeper at the start than 1st, and tailing off more slowly

Question 11

half-life (conc-time)

Answer 11

• 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

Question 12

calculating rate constant from the half-life

Answer 12

k= ln2/ t1/2

Question 13

shape of a zero order rate-conc graph

Answer 13

• horizontal straight-line, with a 0 gradient
• rate=k
• y intercept gives the rate constant k
• rate does not change with increasing conc

Question 14

shape of a first order rate-conc graph

Answer 14

• straight-line graph through the origin
• rate= k[A]
• rate is directly proportional to conc
• k= gradient

Question 15

shape of a second order rate-conc graph

Answer 15

• upward curve with an increasing gradient

- rate= k[A]2

Question 16

iodine clocks

Answer 16

• way of obtaining the initial rate
• relies on the formation of iodine, starch is added- forms blue/black colour in the presence of iodine
• intial rate is proportional to 1/t

Question 17

the rate determining step

Answer 17

the slowest step

-rate equation only includes species involved in the rate determining step

Question 18

the Arrhenius equation

Answer 18

k= A e-(Ea/RT)
A- pre-exponential factor
R- gas constant- 8.314 J mol-1 K-1
T-temp in K

Question 19

logarithmic form of Arrhenius

Answer 19

In K = - Ea/RT + In A

gradient= - Ea/R