12 Rates of Reaction

Slow reaction examples

Rusting of iron

Weathering of rocks

Fermentation

Fast reaction examples

Fireworks

Explosions

Precipitation reaction

Rate of reaction formulae

Rate of reaction

The change in concentration (mole) of reactants or products in unit time (seconds).

Unit: mol s^-1

Ways to measure rate of reaction

• Measuring a change in volume of gas produced over time using a gas syringe - if reaction produces a gas

• Decrease in mass of the reactants can be measured over time - if reaction produces a gas that escapes

• A change in colour intensity, pressure, temperature or pH - if any of these properties change during a reaction

• The appearance of a precipitate - if one is formed in reaction

Conditions needed for a reaction to occur

• Reactant particles must collide with eachother to break their bonds

• They must collide with enough energy to break their bonds and enable new bonds to form (the minimum energy needed is the activation energy)

• Reactant particles must collide with the correct orientation so bonds can break and reform in the required way

Draw a rate curve

Describe what’s happening in a rate curve

At the beginning of the reaction the gradient is steepest showing the rate of reaction is at its highest (there are a lot of particles meaning a lot of collisions can happen)

As the reaction progresses, the curve becomes shallower showing the rate is decreasing (there are less and less reactant particles)

The curve becomes horizontal (the gradient = 0) showing the reaction is complete

Factors that affect rate of reaction

• concentration of reactants

• temperature

• Surface area (particle size)

• Presence of a catalyst

• Pressure and light (for some reactions: pressure - if reactions are gases, light - reactions like photosynthesis)

Draw a rate curve after adding a factor that increases rate of reaction