rate of reaction

techniques for measuring rate of reaction

• mass loss

• gas production

• colorimetry

units of rate of reaction are typically

mol dm^-3 s^-1

calculating rate of reaction

change in concentration/ change in time

what is a colorimeter or spectrometer

measures the light intensity of light passing through a sample, intensity of light is measured every few seconds and data is plotted, light intensity is related to the concentration

measuring the rate of reaction using changes in mass

when gas is produced in a reaction it escapes from the reaction vessel so the mass of the vessel decreases, can be measured using balance, the cotton wool in the neck of the flask allows gas to escape

one limitation of measuring loss in mass

gas must be sufficiently dense or the change in mass is too small to measure on a 2 or 3 decimal balance

measuring rate of reaction using changes in volume of gas

gas collection can involve collecting gas through water by displacement using a burette or inverted measuring cylinder, this method can only work if gas has a low water solubility

collision theory

for a reaction to occur:

• particles must collide with enough kinetic energy

• rate of chemical reaction depends on how often successful collisions happen

what is collision theory affected by

• how often particles collide

• the energy each particle has when they collide

• the minimum energy needed for reaction to occur: activation energy

• collision geometry - orientation or angle when particles collide

what can collision frequency (how often particles collide) be altered by

• change in total pressure

• change in concentration of reactants

• change in temperature

• change in surface area

what affects rate of reaction

• concentration

• pressure

• temperature

• surface area

• catalyst

how does pressure affect rate of reaction

• the same number of particles occupy a smaller volume, resulting in increased collision frequency

how do catalysts impact rate of reaction

they lower activation energy so more particles will have sufficient energy to react

energy profile of exothermic reaction

energy of reactants are higher than products, change in products - reactants is less than 0

energy profile of endothermic reaction

products have higher energy than reactants and change in products - reactants is greater than 0, (positive 🔺H)

in a maxwell boltzmann graph, why do the particles never show having 0 energy ?

there will always be a small amount of particles that have very high energy

how does a catalyst impact the rate of reaction

it provides an alternative pathway for a reaction to occur, lowering the activation energy

how does raising the volume of a reactant impact the rate of reaction

it lowers the rate of reaction because the same amount of particles being in a larger space increases the distance between them, leading to lower frequency of successful collisions

what’s the relationship between the rate and concentration of reactant in a zero order reaction

the rate is independent of the concentration of the reactant → same amount of concentration decomposes over time