Rates

Describe the effect of surface area (of a solid) on rate of reaction

Describe the effect of surface area (of a solid) on rate of reaction

• If the solid is split into several pieces, the surface area increases.

• This results in an increased area for the reactant particles to collide with.

• The smaller the pieces, the larger the surface area. This means more collisions and a greater chance of reaction.

Describe the effects of changes of concentration of a solution on the rate of reaction

• At a higher concentration, there are more particles in the same amount of space.

• The particles are more likely to collide, and therefore more likely to react.

• The higher the concentration of a dissolved reactant, the faster the rate of reaction.

Describe the effect of pressure of a gas on the rate of reaction

• As the pressure increases, the space in which the gas particles are moving become smaller.

• The gas particles become closer together, increasing the frequency of collisions. The particles are more likely to react.

• Therefore, increasing the pressure of gaseous reactants causes rate to increase.

Describe the effect of changes in temperature on the rate of reaction

• Particles have more kinetic energy at higher temperatures.

• Particles collide more frequently.

• More successful collisions occur at or above the activation energy.

• Therefore, rate increases with temperature.

Describe the effect of a catalyst on the rate of reaction

• A catalyst speeds up a reaction without being used up itself.

• It provides an alternative reaction pathway with a lower activation energy.

What is a catalyst?

• A catalyst is a substance that speeds up a reaction, but is chemically unchanged at the end of the reaction.

• It provides an alternative reaction pathway with a lower activation energy.

Describe an experiment to investigate the effects of changes in surface area of a solid on the rate of reaction.

1. weigh a marble chip with a mass between 0.4g and 0.5g.

2. Put hydrochloric acid into a conical flask, with a bung that has a tube going into an upturned cylinder in a water bath.

3. make sure the upturned cylinder is full of water.

4. put the chip into the acid.

5. place bung on flask and shake gently.

6. record volume of gas collected every minute until reaction has stopped. keep the flask well shaken.

7. wash out flask with water.

8. select very small marble chips, that have a total mass of the original marble chip.

9. repeat the experiment, and then do the same process using powdered chalk.

Describe an experiment to investigate the effect of concentration of a solution on rate of reaction

1. mix sodium thiosulfate solution and 10cm3 hydrochloric acid.

2. place the flask over a piece of paper with a cross on it.

3. time how long it takes for the solution to produce enough sulphur to make the solution opaque. Stop the clock when you can no longer see the cross.

4. repeat experiment using different volumes of sodium thiosulfate and water (WATER DILUTES SODIUM THIOSULFATE.)

Equation for concentration experiment

sodium thiosulfate + hydrochloric acid → sodium chloride + sulfur + sulfur dioxide + water

• 1/time

Describe an experiment to investigate the effect of temperature on the rate of reaction

1. measure 10cm3 of hydrochloric acid using a measuring cylinder.

2. pour into boiling tube and record temperature of acid.

3. attach a gas syringe to a delivery tube that goes through the rubber bung of the boiling tube.

4. add 2cm length of magnesium ribbon to acid and replace bung.

5. start a stopwatch and record volume every 10 seconds until volume no longer changes.

6. repeat the experiment, heating the acid at different temperatures (NOT GOING ABOVE 50 degrees Celsius)

Describe an experiment to investigate catalysts using hydrogen peroxide solution

1. put the following substances in a separate test tube:

2. add 2cm3 of hydrogen peroxide solution to each test tube.

3. observe the rate of oxygen bubbles in each tube.

• manganese oxide

• copper oxide

• zinc oxide

• sodium chloride

• 1cm3 peeled potato

• 1cm3 sliced liver

Hydrogen peroxide

Hydrogen Peroxide decomposes very slowly into oxygen and water at room temperature.

What increases rate of reaction?

• more frequent collisions

• more energetic collisions

equation for rate of reaction

change in reactant/time

What 3 things must happen for a reaction to occur?

1. must collide

2. correct orientation

3. enough energy - at or in excess of the activation energy.

What is the activation energy?

The minimum amount of energy needed for the particles to react.

The activation energy is different for each reaction.