Rates of Reaction

Question 1

rate of reaction =

Answer 1

amount of reactant used up / time taken

Question 2

what is activation energy

Answer 2

the minimum amount of energy needed by the reactant particles to react on collision

Question 3

what is an endothermic reaction

Answer 3

heat energy is taken in from the surroundings

Question 4

what is an exothermic reaction

Answer 4

heat energy is given out from the surroundings

Question 5

what happens to the rate of reaction as temperature increases

Answer 5

rate of reaction increases

Question 6

why does rate of reaction increase as temperature increases

Answer 6

when temperature increases the particles move faster so they collide more frequently. Further, the particles collide with greater energy so more of the reactant particles have enough energy greater than activation energy to react on collision. There are more successful collisions per unit time hence the rate of reaction increases

Question 7

how do you increase the temperature

Answer 7

warm the solution / acid

Question 8

how do you increase the surface area of a solid reactant

Answer 8

crush the …. with a pestle and mortar

Question 9

why are three experiments done and not only one

Answer 9

to improve the reliability of the investigation
to identify anomalous results
to be able to calculate an average value

Question 10

how does concentration increase the rate of reaction

Answer 10

when the concentration of a solution is increased there are more reactant particles in the same volume. There is a greater chance of the reactant particles colliding, so the frequency of collisions increases and the rate of reaction increases

Question 11

if hydrogen was being produced, why can the rate of reaction not be measured by measuring the mass of the reactants with time

Answer 11

Hydrogen has a very low molar mass, so the change in mass would be too small to measure

Question 12

what are the 3 ways the volume of gas produced in a reaction can be measured accurately

Answer 12

use a gas syringe

collect the gas over water using an inverted measuring cylinder of water

collect the gas over water using an inverted burette of water

Question 13

new concentration =

Answer 13

volume of acid / total volume x original concentration of acid

Question 14

how can the student control the volume of acid used in each experiment

Answer 14

water can be added to make all the total volumes the same

Question 15

what are the possible causes for an anomalous result for the volume of gas

Answer 15

there was an error in measuring the volume of gas

the conc of acid was incorrect

there was a change in temp

some has escaped from the flask

there was a timing error

there was a plotting error

Question 16

why does pressure increase the rate of reaction

Answer 16

when a pressure is increased the particles are pushed closer together so there are the same number of particles but in a smaller volume. There are more reactant particles per unit volume so the frequency of collisions increases and rate of reaction increases

Question 17

how does surface area increase the rate of reaction

Answer 17

the powder has a larger surface area than the solid so more particles are exposed to the acid particles. There is a greater surface for collisions to take place with the acid particles. The frequency of collisions increases and the rate of reaction increases

Question 18

how does a catalyst speed up the rate of reaction

Answer 18

a catalyst provides an alternative reaction route that requires a lower activation energy. This speeds up the reactions because more of the reactant particles have enough energy, greater than activation energy, to react on collision, so more successful collisions occur.

Question 19

why are catalysts useful in industry

Answer 19

they reduce energy costs

Question 20

what happens to catalysts at the end of a reaction

Answer 20

it remains chemically unchanged and its mass stays the same at the end of the reaction