Rates of reaction and temperature

Question 1

rate of reaction

Answer 1

a measure of how quickly reactants are used or products are formed

Question 2

how do you calculate the rate of a reaction?

Answer 2

amount of reactant used or product formed/ time taken

Question 3

describe the collision theory

Answer 3

particles must collide with enough energy and correct orientation to react successfully

Question 4

what does a change that increases the chances of particles colliding do to the rate of a reaction?

Answer 4

it increases the rate of reaction

Question 5

what is a limiting reactant?

Answer 5

the reactant that is used up first

Question 6

describe the rate of reaction at low temperatures

Answer 6

at low temperatures particles have less kinetic energy, there are less collisions which means the rate of reaction is slower

Question 7

describe the rate of reaction at high temperatures

Answer 7

at high temperatures particles have more kinetic energy, there are more collisions which means the rate of reaction is faster

Question 8

what are the factors that affect the rate of a reaction?

Answer 8

-temperature
-concentration
-pressure (for gases)
-surface area

Question 9

describe the different methods of measuring rates of reaction

Answer 9

-measuring the mass lost as a gas formed is allowed to escape over time (requires a very precise mass balance e.g. 23-4 decimal places)
-collecting a gas formed in a syringe over time (most ideal method)
-timing how long it takes for a solid reactant to disappear (good but may take a long time to get results)
-collecting gas formed in an inverted measuring cylinder full of water in a water bath, over time (not ideal as results are not as accurate and is difficult to set up)
-timing how long it takes for a solution to turn cloudy (due to a solid precipitate forming)

Question 10

why does having lots of small particles instead of one large particle increase the rate of reaction?

Answer 10

because there are more particles at the surface which are available to react with the other substance

Question 11

what happens as surface area to volume ratio is increased?

Answer 11

• there are more particles at the surface exposed to the other reactant
  -more reactant particles are available for collisions, leading to an increase in the frequency of successful collisions
  -the rate of reaction will increase

Question 12

what is the method for the PAG?

Answer 12

1. set up the inverted measuring cylinder full of water in a water tub and insert gas delivery tube
2. measure the mass of some large marble chips and transfer into conical flask
3. measure 25cm^3 of acid
   4.add acid to conical flask, stopper reaction and start timer
4. measure the volume of gas produced in 30 seconds
5. repeat for the same mass of small marble chips

Question 13

which was the faster reaction for the PAG and why?

Answer 13

The small chips were faster as they had a larger surface area. This meant that more particles were exposed at the surface to the reactant which meant that more reactant particles were available for collisions leading to an increase in the frequency of successful collisions.

Question 14

what could you say about the volume of gas collected from both experiments by the end of the reaction?

Answer 14

The volume would be the same as it was the same mass of reactant so the same volume of gas would be produced.

Question 15

How could you improve the method used and therefore improve your results?

Answer 15

We could use a gas syringe for more accurate measurements of gas.

Question 16

how does the concentration of a solution affect the rate of reaction?

Answer 16

If the concentration of a solution is increased:
-there are more reactant particles in a fixed volume
-particles are more crowded
-particles are likely to collide more often, leading to a greater frequency of successful collisions
-rate of reaction increases

Question 17

how dos the pressure of the reacting gas effect the rate of reaction?

Answer 17

If the pressure of reacting gases is increased:
-the volume decreases (but the number of particles stay the same)
-particles are more crowded
-particles are likely to collide more often, leading to a greater frequency of successful collisions
-rate of reaction increases

Question 18

what is the method for the PAG measuring rates of reaction?

Answer 18

1. put 50cm^3 of sodium thiosulfate solution in a flask
2. measure 10cm^3 of dilute hydrochloric acid in a 10cm^3 measuring cylinder
3. add the acid to the flask and immediately start the clock, swirl the flask to mix the solutions and place it on a piece of paper marked with a cross
4. look down at the cross from above, when the cross disappears stop the clock and record the time in the table
5. repeat using different concentrations of sodium thiosulfate solution, make up to 50cm^3 of each solutions, mix different volumes of the sodium thiosulfate solution with water
6. dispose of waste into the stop bath to neutralise the acid to prevent SO2 production

Question 19

what are the healthy and safety risks for the measuring rates of reaction PAG?

Answer 19

-HCl is an irritant (safety goggles/handle with care)
-SO2 is a respiratory irritant (ventilate room/stop the reaction)
-disposal of whole solutions (stop bath or back into containers)

Question 20

what trend can you deduce from the measuring rates of reaction PAG graph?

Answer 20

as the concentration of sodium thiosulfate increases, the rate of reaction increases

Question 21

explain the trend deduced from the measuring rates of reaction PAG graph

Answer 21

a higher concentration has more particles per unit volume; particles are more crowded which increases the frequency of successful collisions

Question 22

what are the independent, dependent and control variables in the measuring rates of reaction PAG?

Answer 22

independent- concentration of sodium thiosulfate solution
dependent- reaction rate/time taken for cross to disappear
control- volume of hydrochloric acid and total volume of sodium thiosulfate solution, same conical flask, same cross

Question 23

what could have caused inaccurate results in the measuring rates of reaction PAG?

Answer 23

-difficult to judge exactly when cross disappears (subjective)
-conical flask wasn’t dried between tests (concentration isn’t accurate)
-small spillages
-timing inconsistent

Question 24

suggest some improvements for the measuring rates of reaction PAG?

Answer 24

-use a colourimeter (uses light intensity)
-use a burette and a pipette