M3 ,, Reeaction Rates

Question 1

Collision theory?

Answer 1

Reactions can only occur when collisions take place between particles having sufficient energy. The energy is usually needed to break the relevant bonds in one or either of the reactant molecules.
This minimum energy is called the Activation Energy

Question 2

Higher concentration + pressure?

Answer 2

higher concentrations(and pressures) there are more particles per unit volume and so the particles collide with a greater frequency and there will be a higher frequency of effective collisions.

Question 3

Rate of reaction?

Answer 3

change in concentration of a substance in unit time Its usual unit is mol dm-3s-1

Question 4

Catalyst?

Answer 4

Catalysts increase reaction rates without getting used up.
Explanation: They do this by providing an alternative route or mechanism with a lower activation energy so more molecules have energy above activation energy.

Question 5

Heterogeneous catalyst?

Answer 5

A heterogeneous catalyst is in a different phase from the reactants

Question 6

A homogeneous catalyst?

Answer 6

A homogeneous catalyst is in the same phase as the reactants

Question 7

Benefits of catalyst?

Answer 7

Catalysts speed up the rate of reaction. This means that the use of a catalyst may mean lower temperatures and pressures can be used.
This can save energy costs as there is reduced energy demand for providing high temperature and less electrical pumping costs for producing pressure.
This can mean fewer CO2 emissions from burning of fossil fuels.

Question 8

Teach inquest to investigate rates of reaction?

Answer 8

measurement of the change in volume of a gas

Measurement of change of mass

Colorimetry

Measuring change in electrical conductivity

Question 9

measurement of the change in volume of a gas?

Answer 9

This works if there is a change in the number of moles of gas in the reaction. Using a gas syringe is a common way of following this.
(CH3)2C=CH2(g) + HI(g) (CH3)3CI(g)
HCOOH(aq) + Br (aq)  2H+(aq) + 2Br - (aq) + CO (g)

Question 10

Measurement of change of mass?

Answer 10

This works if there is a gas produced which is allowed to escape. Works better with heavy gases such as CO2

Question 11

Titrating samples of reaction mixture with acid, alkali, sodium thiosulphate etc?

Answer 11

1. Small samples are removed from the reaction mixture
2. quench (which stops the reaction)- can be done by
   • by dilution with water
   • by cooling
   • by adding a reagent that reacts with one of the reactants
3. then titrate with a suitable reagent.

The NaOH could be titrated with an acid The H+ could be titrated with an alkali
The I2 could be titrated with sodium thiosulphate

Question 12

Colorimetry?

Answer 12

one of the reactants or products is coloured then colorimetry can be used to measure the change in colour of the reacting mixtures

Question 13

Measuring change in electrical conductivity?

Answer 13

Can be used if there is a change in the number of ions in the reaction mixture

Question 14

Maxwell Boltzmann Distribution?

Answer 14

The Maxwell-Boltzmann energy distribution shows the spread of energies that molecules of a gas or liquid have at a particular temperature

Question 15

MBD - increasing temp?

Answer 15

energy of the particles increases. They collide more frequently and more often with energy greater than the activation energy. More collisions result in a reaction

Question 16

MBD - JNCREASING SA?

Answer 16

particles and this increases the rate of the reaction.
Increasing surface area will cause collisions to occur more frequently between the reactant

Question 17

MBD - effect of catalyst?

Answer 17

If the activation energy is lower, more particles will have energy > EA, so there will be a higher frequency of effective collisions. The reaction will be faster