Rates Of Reaction

Question 1

Rate of reaction equation and units

Answer 1

Rate equals 1 over time, units = s-1

Question 2

Rate of reaction determined by

Answer 2

Loss of a reactant over time
Gain of a product over time

Question 3

Reactions used in rate of reaction experiments

Answer 3

1. Metals with dilute acid,The volume of hydrogen gas produced/the mass of gas lost over a given period of time.E.g Mg +2HCl -> MgCl2 + H2
2. Marble Chips with dilute acid,The volume of carbon dioxide produced/the mass of carbon dioxide lost over a given period of time.E.g CaCO3 + 2HCl -> CACl2 + CO2 + H2O
3. Catalytic decomposition of hydrogen peroxide, in the presence of manganese(IV)oxide. 2H2O2 -> 2H2O + O2. The volume of oxygen produced/the mass of oxygen lost over a given period of time.
4. Sodium thiosulfate with acid forms a perciptate of sulfur. 2HCl(aq) +
   Na2S2O3(aq) —> 2NaCl(aq) + SO2(g) + S(s) + H2O(l). Time taken to form a certain amount of precipitate can be measured.

Question 4

Measuring volume of gas produced per unit time

Answer 4

Stopwatch started- gas collected in gas syringe. Vol of gas measured and recorded at various time intervals. Reaction over-two readings are the same as on more gas is being produced.

Question 5

Measuring change in mass in a given time

Answer 5

If the reaction produces a gas- mass decrease as the gas has escaped from flask to atmosphere. As cotton wool plug allows gas out but prevents any loss of liquid if bubbling occurs.

Question 6

Formation of a precipitate

Answer 6

2 aqueous solutions mixed(sometimes a precipitate forms). Place the reaction flask(containing one reactant solution) on top of a piece of with a x draw on on it. The time recorded when the second solution is added until the precipitate forms and obscures the x from the view of a observer who is looking down into the flask.

Question 7

Activation energy

Answer 7

Minimum energy needed for a reaction to occur

Question 8

Collision theory

Answer 8

Reactant particles move towards each other, they collide and connect, then the product particles move away from each other.

Question 9

Catalyst

Answer 9

A substance that increases the rate of reaction without being used up itself.

Question 10

Factors affecting the rate of reaction

Answer 10

1.Temperature- Increases rate of reaction- particles move faster, more frequent collisions, have more energy so have the activation energy when they collide. So more successful collisions between particles in a given period of time.
2.Concentration of solution. Increases rate of reaction- more particles present in the same volume, more successful collisions(with activation energy) between particles in a given period of time.
3. Surface area of solids- Increases rate of reaction- more particles on surface exposed to other reactants, more successful collisions(with activation energy) between particles in a given period of time.
4. Presence of a catalyst- provides an alternative pathway of lower activation energy. More successful collisions between particles in a oven period of time.