Rates Of Reaction

Question 1

How do you measure rate of reaction with marble chips and hydrochloride acid

Answer 1

Weigh 10g marble chips into conical flask and pour 20cm3 of dilute hydrochlorid acid into a measuring cyclinder and pour into flask then use bung and gas syringe into clamp stand and delivery tube and record volume of c02 every 10 seconds

Question 2

How is knowing rate of reaction helpful

Answer 2

Rusting - slow reaction sped up by moisture salt and warm climate
Unwanted reactions slowed down by temperature control like milk in a fridge is stopped souring

Question 3

What are 5 ways of measuring rates

Answer 3

• gas syringe
• cotton wool bung to allow gas to escape and record a change of mass
• exothermic or endothermic reactions you can record a change in temperature
• time taken for precipitate to obscure a mark placed below reaction vessel
• change in colour of a solution maybe followed

Question 4

Average rate equation

Answer 4

Time taken

Question 5

How do you find rate at exact moment

Answer 5

Draw tangent to the point on the graph then find gradient of tangent by change in y/ change in x

Question 6

What is collision theory and how does explain shape of reaction graph of marble chips and hcl

Answer 6

Rate of chemical reaction is proportional to the rate of successful collisions . In order for particles to react they must collide with sufficient energy and in the correct orientation. Any change in conditions that result in an increase of frequency of collision will increase rate of reaction. So as acid particles react and get used up colliding with the marble chips the collision rate decreases and the reaction slows down as there are less acid particles left and the marble is in such excess that it’s shape doesn’t change much

Question 7

How does decreasing surface Area of solid reactant affect rate of reaction

Answer 7

There is a greater target area in contact with the reactant and a grater area that collisions can take place so there are more collisions per second so larger rate of reaction

Question 8

How does concentration of liquid reactants affect rate of reaction

Answer 8

Increases more reactant particles in the same volume so collision is more likely so there will be more collisions per second so then a greater rate , same with gases pressure as the amount of gas is compressed into smaller volume so more gas particles / cm3. Doubling concentration doubles reaction rate , often concentration is directly proportional to reaction rate.

Question 9

What does changing volume of reactant do

Answer 9

Doesn’t effect rate only increased the amount of product

Question 10

What does an increase of 10 c do to rate usually

Answer 10

Doubles the rate

Question 11

Why does temperature affect rate

Answer 11

Kinetic energy of particles incaresed so they move faster so there are more collisions
( slight increase in rate ) Also means that more collisions will occur with an energy excess of the activation rmeber by resulting in more successful colisions. Increases proportion of particles with energy grater than the activation energy (larger increase in rate )

Question 12

What is activation energy

Answer 12

Minimum energy required for the bonds to be broken resulting in successful collision between colliding particles , different for diffrent particles . If particles are moving too slowly they will bounce apart without reacting

Question 13

What does changing has pressure do

Answer 13

Only makes a different In gases as smaller pressure means gas particles are closer to each other so hit each other more frequently

Question 14

What is a catalyst

Answer 14

SubsTance that increases the rate of a chemical reaction without being used up in the overall reaction. It will have same mass at beginning and end of reaction

Question 15

How does a catalyst work

Answer 15

Brings the reactant molecules on its surface ( why a powdered catalyst is most effective because it has a large surface area). This weakens the bonds in reactant molecule so less energy is required to break them and a lower activation energy is possible . Provides an alternative pathway for a reaction with a lower activation energy . Doesn’t lower activation energy just provides an easier alternative . Because activation energy is lower there will be more successful collisions

Question 16

How do you investigate the catalysis of the decomposition of hydrogen peroxide

Answer 16

It decomposes slowly at room temp producing ocupen and water . Prepare hydrogen peroxide solution of 2cm3 of hydrogen peroxide and 48 cm3 of water in a beaker put this in 5 test tubes in a test tube rack add catalysts and collect oxygen in a gas syringe at regular intervals to get rate of reaction .

Question 17

How do you prove a substance is a catalyst

Answer 17

Weigh catalyst before , then separate it from liquid by filter it through filter paper and allowing paper and residue to dry and the mass will be unchanged

Question 18

What are enzymes

Answer 18

Biological catalysts , more effective than inorganic catalysts and highly specific e.g brewing enzymes produced by yeast catalyse the breakdown of glucose into ethanol and carbon dioxide

Question 19

How are catalysts used in industry’s

Answer 19

Make substances react quicker at lower temperatures and pressure than would otherwise be needed , saving money