Collision Theory - 4th

Question 1

when can a chemical reaction only happen?

Answer 1

• if the reactant particles collide with enough energy

Question 2

what is activation energy?

Answer 2

• the amount of energy the particles need to react is called activation energy

Question 3

what will happen to particles which collide with less energy than the activation energy?

Answer 3

• will just rebound and remain unchanged

Question 4

what does the overall rate of reaction involving millions of particles depend on?

Answer 4

• collision frequency
• percentage success

Question 5

what is collision frequency?

Answer 5

• how often do the particles collide with each other

Question 6

what is percentage success?

Answer 6

• what percentage of the collisions have enough energy?

Question 6

what are four common factors which affect rate of reaction?

Answer 6

• surface area
• concentration
• temperature
• catalysts

Question 6

why does a higher solid surface area increase the rate of reaction?

Answer 6

• more of the solid is exposed to the other particles
• so the collision frequency is higher
• so there are more successful collision per unit time

Question 6

why does a higher temperature a increase the rate of reaction?

Answer 6

• the particles have more kinetic energy
• so the percentage of collisions with enough energy is higher
• so there are more successful collisions per unit time

Question 7

why does a higher solution concentration/gas pressure increase the rate of reaction?

Answer 7

• there are more particles per unit volume
• so the collision frequency is higher
• so there are more successful collisions per unit time

Question 7

why does a catalyst increase the rate of reaction?

Answer 7

• they provide an alternative route with a lower activation energy
• so the percentage of collisions with enough energy is higher
• so there are more successful collisions per unit time

Question 8

how can you increase the concentration of a solution/gases?

Answer 8

• by dissolving more solute particles

Question 9

how can you increase the pressure of a solution/gases?

Answer 9

• by making the reaction vessel smaller

Question 10

how can the effect of concentration on rate be demonstrated?

Answer 10

• by reacting sodium thiosulphate solution with hydrochloric acid to make sodium chloride, sulphur solid , sulphur dioxide and water

Question 11

what is the chemical equation for the disappearing cross experiment?

Answer 11

• Na2S2O3 (aq) + 2HCl (aq) -> 2NaCl (aq) + S (s) + SO2 (g) + H20

Question 12

describe the observations of the disappearing cross experiment?

Answer 12

• in this reaction, a solid (sulphur) is slowly produced
• after a while, you cannot see through the mixture any longer
• this is measured by observing a black cross under the mixture

Question 13

what are the variables for the disappearing cross experiment?

Answer 13

• input : the concentration of the Na2S2O3 (aq)
• output : the time taken for the cross to disappear
• control : total volume of solution, concentration of HCl (aq), temperature

Question 14

how is rate calculated?

Answer 14

• rate (s^-1) = 1/time taken (s)

Question 15

what is the relationship between rate and concentration?

Answer 15

• they are proportional

Question 16

how is surface area increased?

Answer 16

• by cutting or grinding up the solid

Question 17

how is the effect of surface area on rate demonstrated?

Answer 17

• by reacting calcium carbonate marble chips with hydrochloric acid to form calcium chloride, water and carbon dioxide gas

Question 18

what is the chemical equation for the marble chip experiment?

Answer 18

• CaCO3 (s) + 2HCl (aq) -> CaCl2 (aq) + H2O (l) + CO2 (g)

Question 19

what are the variables in the marble chip experiment?

Answer 19

• input : the sizes of the CaCO3 (s) chips
• output: the volume of CO2 (g)
• control: the mass of CaCO3(s), the volume and concentration of HCl (aq), temperature

Question 20

how is the volume of carbon dioxide measured in the marble chip experiment?

Answer 20

• using a gas syringe or inverted measuring cylinder in water

Question 21

what are the results of the marble chip experiment on a graph of volume of CO2 against time?

Answer 21

- a higher SA has a steeper start than the one with a lower SA because the rate has increased, so the volume of CO2 is increasing faster - it has the same final volume of CO2- this is because the total amount of reactants hasn't changed, so eventually the reaction produces the same amount of CO2

Question 22

how can temperature be increased?

Answer 22

- by heating

Question 23

how can the effect of temperature on rate be demonstrated?

Answer 23

- by reacting magnesium with hydrochloric acid to produce magnesium chloride and hydrogen gas

Question 24

what is the chemical equation for the magnesium and acid experiment?

Answer 24

- Mg (s) + 2HCl (aq) -> MgCl2(aq) + H2

Question 25

describe what happens in the magnesium and acid reaction?

Answer 25

- the magnesium disappears

Question 26

what are the variables in the magnesium and acid experiment?

Answer 26

- input: the temperature of the HCl (aq) - output: the time taken for Mg (s) to disappear - control: mass and SA of Mg (s) and the volume and concentration of HCl (aq)

Question 27

what are the results of the magnesium and acid experiment on a graph of rate against temperature?

Answer 27

- rate isn't proportional to temperature so it isn't a straight line - it doesn't go through the origin because the rate isn't zero at 0 degrees

Question 28

what are catalysts?

Answer 28

- are substances (usually solids) which increase rate and remain chemically unchanged

Question 29

how can the effect of a catalyst on rate be demonstrated?

Answer 29

- using the decomposition of hydrogen peroxide - 2H2O2 (aq) -> 2H2O (l) + O2 (g)

Question 30

describe the results of the hydrogen peroxide experiment?

Answer 30

- very very slow reaction, usually taking days to finish - it is catalysed by manganese (IV) oxide (MnO2), which is a black solid - this causes it to place much faster, taking only a few seconds to finish

Question 31

what are the variables of the hydrogen peroxide experiment?

Answer 31

- input: which catalyst is being used - output: volume of O2 (g) - control: volume and concentration of H2O2 (aq), temperature, mass and surface area of catalyst

Question 32

what are the results of the hydrogen peroxide experiment on a graph of volume of O2 gas against time?

Answer 32

- increases - most effective catalysts increase rate more effectively - results in a steeper line on the graph - the initial volume of the reactants is the same, so all lines would eventually flatten out at the same total volume of O2 (g) if you waited long enough - the MnO2 (s) - catalysed decomposition of hydrogen peroxide is used to produce oxygen in the lab