chemistry paper 2 - REACTIONS

Question 1

How do you calculate mean rate of reaction

Answer 1

quantity of reactants used or quantity of products formed divided by time taken

Question 2

What does collision theory state

Answer 2

collision theory states that reactions can only occur if particles collide. These particles must also collide with sufficient energy in order to form new substances in the products. The minimum amount of energy required in order for these particles to react is called the activation energy.

Question 3

what are the main 2 ways that rate of reaction increases

Answer 3

increase in the frequency of which particles collide with each other
increase in the amount of energy for the colliding particles

Question 4

does a powder or a solid react faster

Answer 4

by breaking a larger piece of solid into smaller pieces new surfaces are exposed and hence surface area to volume ratio has increased. As there is more given area for particles to collide and react we can say frequency of collisions will increase in the same period of time. Therefore rate of reaction will increase and this fine powder will react faster than an equal mass lumps of the substance.

Question 5

how does increasing the temperature affect rate of reaction

Answer 5

by increasing temperature both frequency of collisions will increase and the reacting particles will collide with increased energy therefore a higher proportion of reacting particles will exceed activation energy and increase rate of reaction

Question 6

how does concentration and pressure effect rate of reaction

Answer 6

by increasing the concentration of reactant particles within a solution you increase rate of reaction because more particles of reactants will move around in the same volume of solution . This will increase frequency of collisions and thus rate of reaction
by increasing the pressure effectively the gas particles will be squashed and compacted closer together. this means that there will be a higher proportion of gas particles per given unit of volume or space and such will increase frequency of collisions which will then increase rate of reaction

Question 7

how can you measure rate of reaction. What principal does this follow. list the steps accurately
(disappearing cross experiment)

Answer 7

• using a measuring cylinder add 10cm3 of sodium thiosulphate to a conical flask
• place conical flask over printed black cross
• using a different measuring cylinder add 10cm3 of hydrochloric acid to a conical flask
• stir to mix contents and start a stopwatch
• look at solution from top of the conical flask
• stop stopwatch when solution has turned cloudy, yellow precipitate has formed and the black cross is no longer visible
• repeat the experiment using lower concentrations of sodium thiosulphate solution
• calculate and plot mean values for each concentration of sodium thiosulphate solution

this experiment works because the sodium thiosulphate reacts with hydrochloric acid to produce sulphur and hydrogen which as sulphur is a solid and hydrogen is clear and will turn solution cloudy

• the problem with this is that different people have different eyesight’s and their cross might disappear before other people

Question 8

how can you measure rate of reaction using volume . what principal does this follow. list the steps accurately

Answer 8

• add 50cm3 of hydrochloric acid to a conical flask using a measuring cylinder
• attach a bung and delivery tube to conical flask
• place delivery tube into a beaker of water
• place an upturned measuring cylinder also containing water over delivery tube
• add a 3cm strip of magnesium to hydrochloric acid this reaction will produce hydrogen gas
• this hydrogen gas will then be trapped in the measuring cylinder
• record the volume of hydrogen gas produced every 10 seconds until no more is produced
• repeat the experiment using different concentrations of hydrochloric acid

Question 9

what does a catalyst do

Answer 9

a catalyst increases the rate of reaction and is not used up remaining chemically unchanged so can be used multiple times. Different catalysts are needed for different reactions. A catalyst works by increasing rate of reaction by providing an alternative reaction pathway so a higher proportion of particles of reactants will collide with sufficient energy and thus increase frequency of effective collisions (successful) and increase rate of reaction

Question 10

why might catalysts be used in industrial processes

Answer 10

catalysts decrease the amount of energy and time needed for a reaction to occur and therefore can reduce cost and impact on environment

Question 11

what do we class a reversible chemical reaction and how do we define this

Answer 11

a reversible chemical reaction is a reaction that involves the breaking down of the products/reaction of them to reform into the original products. within a reversible reaction in the forward and reverse reaction has equal but opposite energy transfers. Meaning that if one direction in a reversible chemical reaction is endothermic the other is exothermic and also the amount of energy absorbed in the endothermic reaction is equal to the amount of energy released in the exothermic reaction

Question 12

what do we define as equilibrium and what is the only way it can be reached

Question 13

what is La chatline’s principle

Question 14

how does increasing/decreasing temperature/pressure affect point of equilibrium or reaction as a whole