C8

Activation energy?

the minimum amount of energy needed for the particles to react when colliding

Rate of reaction?

speed of a chemical reaction

Rate of reaction measures...

a change in either reactants or products

Ways to measure rate of reaction

how long reaction takes to complete (timing), how quickly a reactant is used up, how quickly a product is made

Factors that affect rate of reaction

temperature, pressure, concentration

For a reaction to take place:

particles must collide and collisions must have enough energy to meet the activation energy

As temperature increases...

particles have more energy --> they move faster --> collide more often --> each collision has more energy to meet the activation energy

As surface area increases...

more particles available for collision --> particles collide more often --> each collision has the same energy so there's no change to the activation energy

Catalysts

Substances that change the rate of reaction (speeds up) without being chemically changed themselves

How do catalysts speed up reactions?

They offer alternative pathways with a lower activation energy leading to a higher proportion of reactant particles having sufficient energy to react

Advantages of catalysts in industry

1. Cheaper to use catalysts instead of paying for extra energy

2. saves environment: higher temps/pressure often involve burning fossil fuels --> conserve non-renewable resources

3. catalyst doesn't get used up

Disadvantages of catalysts in industry

1. Same rate of reaction without catalyst - use higher temps/pressures

2. catalysts can become 'poisoned' in chemical plants and don't work anymore - impurities in reaction mixture combines with the catalyst

3. catalysts are often expensive metals

Energy change

the difference in energy between reactants and products

How to calculate overall rate

(final amount (when reaction stops) - starting amount at 0 seconds) divided by

(final time (when reaction stops) - original time (prob. 0))

or draw line from start to end and find gradient

How to calculate rate in a certain time period

(final amount at certain time - amount where time period starts)/(final time - time where time period starts)

How to calculate instantaneous rate of reaction

Draw tangent at particular point and calculate the gradient of the tangent

Method of the concentration vs rate of reaction practical

1. Measure 5ml of sulphuric acid into a test tube using a measuring cylinder

2. Measure 5ml of desired concentration of hydrogen peroxide

3. Mix solutions together

4. Measure 5ml of potassium iodide into a test tube using a measuring cylinder

5. Combine solutions + start stop clock

6. Stop stop clock when solution turn blue/black

7. Repeat for all concentrations

How do you ensure the experiment is fair?

By keeping all the variables the same except from the ones you're testing

Problem: Heat lost to surroundings Improvement?

Use insulation/lid/polystyrene cup

Problem: Measuring cylinder not accurate Improvement?

Use a burette or pipette

Problem: Reaction timed by eye Improvement?

Use a data logger or a stopwatch

Problem: Only one trial Improvement?

Repeat experiment and calculate the mean

Problem: Not all gas collected Improvement?

Use a gas syringe with a tight seal

Problem: Colour change judged by eye Improvement?

Use a colorimeter

How to reduce a random error?

Repeat measurements several times and calculate and average from them

How to reduce reading erros

Use a more precise device with smaller measuring intervals and therefore less uncertainty

How to reduce systematic errors

Instruments should be recalibrated, or different instruments should be used. Correction/adjustments should be made to technique

How to account for zero errors

Take the difference of the offset from each value, the offset could be positive or negative

How to make a measurement more precise

Make the measurements to a greater number of decimal places

How to get a better accuracy and why this helps

Accuracy can be increased by repeating measurements and finding the mean of results. Helps identify anomalies that can be omitted in final results

What is reliability

A measure of the ability of an experimental procedure to produce the expected results when using the same method + equipment

What is validity

A measure of the suitability of an experimental procedure to measure what it is intended to measure

How to get a better validity

Any variables that may affect the outcome are identified + controlled