Reaction rate, collision theory and activation energy

Question 1

the rate of a chemical reaction is determined b the change

Answer 1

in concentration of a reactant or a product per unit time

Question 2

rate of reaction=

Answer 2

(change in concentration) divided by (time for change to happen)

Question 3

to measure the rate of reaction, we need to know (2 items)

Answer 3

• how fast one of the reactants in being used up

- how fast one of the products is being formed

Question 4

in a graph displaying the concentration of a reactant against time, the gradient shows

Answer 4

the rate of reaction

Question 5

we can see the reaction is complete when the gradient on a graph is = to

Answer 5

0, where the gradient is parallel to the x axis (flat)

Question 6

when the curve on a graph is curved, we draw a………and use the equation Gradient=………….to find the rate of direction

Answer 6

tangent (straight line which touches the curve at on point) and Gradient= y / x to find rate of reaction

Question 7

if the unit of concentration is moles per cubic decimetre, and time in secs, then the unit for rate will be

Answer 7

mol dm-3 s-1

Question 8

the rate of reaction can also be calculated by measuring the time it takes for a known……………of product/ reactant to be…………/………………. and the equation rate=……………………….used

Answer 8

the rate of reaction can also be calculated by measuring the time it takes for a known AMOUNT of product/ reactant to be PRODUCED/USED UP and the equation rate= AMOUNT COLLECTED/USED UP / TIME TAKEN used

Question 9

if it takes 40 seconds to collect 20 cm3 of gas, the the rate of reaction was:

Answer 9

rate= amount / time
rate= 20 / 40 = 0.5 cm3 s-1

Question 10

collision theory is the idea that

Answer 10

molecules have to collide in order to react, but even then a collision does not mean that a reaction will occur. the collision has to be successful in order to result in a reaction

Question 11

the two requirements for a collision between two molecules to be successful are:

Answer 11

• the two molecules must collide with sufficient energy to cause a reaction (activation energy)
• the two molecules must collide in the correct orientation

Question 12

activation energy is

Answer 12

the minimum energy that colliding particles must possess for a reaction to occur, E(a)

Question 13

the symbol for activation energy is

Answer 13

E(a)

Question 14

only collisions with equal or greater…………………will result in a reaction

Answer 14

activation energy

Question 15

all chemical reactions involve (in terms of bonds)

Answer 15

breaking and making new bonds

Question 16

breaking bonds ….energy while making new ones…………..energy

Answer 16

requires, releases for new bonds

Question 17

activation energy is involved in

Answer 17

breaking some of the original bonds

Question 18

where collisions are of relatively low energy, the bond-breaking process will

Answer 18

not occur

Question 19

orientation affects whether a reaction will occur because

Answer 19

if two molecules collide so that the groups or atoms involved do not ‘touch’, then no reaction occurs. therefore collisions have to be of both high enough energy and correct orientation so that a reaction occurs

Question 20

a ‘steric factor’ is when

Answer 20

the shapes of molecule influences reactions

Question 21

‘steric hindrance’ in when

Answer 21

atoms or groups of atoms in the reacting molecule physically hinder the reaction through the blocking of attacking species