The Rate and Extent of Chemical Change

Factors affecting rates of reaction

Collision Theory

How frequent the particles collide

The energy transferred during a collision.

Particles must collide with enough energy (activation energy)

Temperature

Concentration of solution

pressure of gas

surface area

catalysts

The particles will move faster

more collisions per second

The faster they move, the more energy they have (more successful collisions)

Same number of particles in the same volume

More collisions per second

More particles in the same volume

Provides an alternative pathway with lower activation energy

Powders have a greater surface area to volume ratio than lumps

More frequent collisions

Measuring Rates of Reaction

Precipitation and colour change

  1. Measure out 10cm3 of sodium thiosulfate with a measuring cyclinder
  1. Fill conical flask with ST
  1. Place the conical flask on a printed black cross
  1. Add 10cm3 of hydrochloric acid into the conical flask
  1. Swirl the solution and start the stopwatch
  1. Stop the clock when you can no longer see the cross (the solution will turn cloudy)
  1. Repeat the experiment again using lower concentrations

Repeat the whole experiment to take mean values

Reproducible: repeated by another person using a different technique and still get the same result

People have different eyesights so will stop the clock at different times

Change in mass

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Volume of gas produced

  1. Use measuring cylinder to place 50cm3 of hydrochloric acid into a conical flask
  1. Attach conical flask to a bung and delivery tube
  1. Place delivery tube into container filled with water
  1. Place an upturned measuring cylinder filled with water into the delivery tube
  1. Add a 3cm strip of magnesium to the hydrochloric acid and start the stopwatch
  1. Every 10 seconds, measure the volume of hydrogen gas trapped in the upturned measuring cylinder
  1. Repeat the experiment using different concentrations of hydrochloric acid

Reversible Reactions

Hydrated copper sulfate ⇌ anhydrous copper sulfate + water

Endothermic

Exothermic

The reaction gets hot as energy is released

Forward reaction takes place when you heat it (putting energy in)

Dynamic Equilibrium

Le Chatelier's Principle

Equilibrium is when the forward and reverse reactions take place at the same rate

If the conditions are changed in a reversible reaction at equilibrium then the system will try to counteract the change

Concentration

Temperature

Pressure

Concentration of products is increased

The reverse reaction if favoured so more reactants are produced

Concentration of products is decreased

The forward reaction is favoured so more products are produced

Temperature increases

Endothermic reaction if favoured

Temperature decreases

Exothermic reaction is favoured

Pressure increases

The reaction the fewer molecules is favoured

Pressure decreases

The reaction with the larger number of molecules

Number of molecules = coefficient

If the number of molecules on either side of the reaction are the same, pressure doesn't have an effect