C3 Rates of Reactions

Question 1

what is the rate of reaction

Answer 1

• amount of reaction used over time - amount of product formed over time

Question 2

how do we measure the rate of reaction

Answer 2

1. mass –> mass may decrease when reaction occurs, (from loss of gas products) mass can be recorded and measured at equal time intervals 2. Volume of gas –> gas collected, volume measured and recorded at regular intervals (w/ gas syringe) 3. light transmissions –> when a precipitate (insoluble solid) is formed the time taken for a cross under the reaction mixture to “disappear” is measured

Question 3

what is the activation energy

Answer 3

the minimum energy required for a reaction to happen

Question 4

what does the rate of reaction depend on

Answer 4

the frequency of collisions the energy of collisions

Question 5

what is the collision theory

Answer 5

when particles collide with enough energy (activation energy) a reaction between them occurs.

Question 6

what happens when particles move faster

Answer 6

they collide with more energy collide more frequently

Question 7

what happens to rate of reaction when surface area is increased

Answer 7

it increases

Question 8

why does the rate of reaction increase when the surface area increases

Answer 8

more of the reactant is exposed - increases frequency of successful collisions

Question 9

what is an independent variable

Answer 9

thing you change

Question 10

what is a dependent variable

Answer 10

thing you measure

Question 11

what is a control variable

Answer 11

what you keep the same

Question 12

what is the concentration

Answer 12

number of particles in a given volume

Question 13

what happens to the rate of reaction when concentration is increased

Answer 13

it increases

Question 14

why does the rate of reaction increase when concentration is increased

Answer 14

more reactant particles moving around the same volume more crowded together so a collision is more likely

Question 15

what happens to the rate of reaction when the temperature is increased

Answer 15

it increases

Question 16

why does the rate of reaction increase when the temperature increases

Answer 16

more kinetic energy is given to particles in form of heat move faster - increased frequency of successful collisions big effect because increasing temp also increases the energy AND frequency of collisions.

Question 17

what is a catalyst

Answer 17

a substance that increases the rate of reaction without itself being used up in the reaction

Question 18

how does a catalyst work

Answer 18

it lowers the activation energy of the reaction - increases the frequency of successful collisions

Question 19

why are only tiny amounts of catalyst required

Answer 19

because thedont get used up

Question 20

why are catalysts important industry

Answer 20

the allow rates of reaction to be increased - helps reduce the cost of various process when a catalyst is present you can use lower temperatures and pressures

Question 21

word equation of the decomposition of hydrogen peroxide

Answer 21

hydrogen peroxide -> water + oxygen

Question 22

symbol equation of decomposition of hydrogen peroxide

Answer 22

2H2O2 ->2H2O+O2

Question 23

example of a catalyst

Answer 23

manganese (IV) oxide - MnO2

Question 24

example of a reaction with requires a catalyst

Answer 24

decomposition of hydrogen peroxide