5.6 The Rate and Extent of Chemical Change (5.6.1 Rate of Reaction (5.6.1…
5.6 The Rate and Extent of Chemical Change
Chemical reactions can occur at vastly different rates. Whilst the reactivity of chemicals is a signi cant factor in how fast chemical reactions proceed, there are many variables that can be manipulated in order to speed them up or slow them down. Chemical reactions may also be reversible and therefore the effect of different variables needs to be established in order to identify how to maximise the yield of desired product. Understanding energy changes that accompany chemical reactions is important for this process. In industry, chemists and chemical engineers determine the effect of different variables on reaction rate and yield of product. Whilst there may be compromises to be made, they carry out optimisation processes to ensure that enough product is produced within a suf cient time, and in an energy-effcient way.
5.6.1 Rate of Reaction
Catalysts increase the rate of reaction by providing a different pathway for the reaction that has a lower activation energy.
Enzymes act as catalysts in biological systems.
Different reactions need different catalysts.
Catalysts change the rate of reaction but are not used up during the reaction.
126.96.36.199 Collision Theory and Activation Energy
Temperature is the average kinetic energy of particles, so increasing the temperature increases the frequency of collisions and makes the collisions more energetic, increasing the rate of reaction.
Increasing the concentration of reactants in solution, the pressure of reacting gases, and the surface area of solid reactants increases the frequency of reactions and so increases the rate of reaction.
The minimum amount of energy that particles must have to react is called the activation energy.
Chemical reactions can only occur when reacting particles collide with each other with sufficient energy.
Collision theory explains how various factors affect the rates of reactions.
188.8.131.52 Factors Affecting the Rate of Reaction.
Presence of a catalyst
Surface area to volume ratio
Pressure of reacting gases
Concentraion of reactants in solution
184.108.40.206 Calculating Rates of Reactions
The units of rate of reaction may be given as g/s, cm^/s , or mol/s.
The quantity of a reactant / product can be measured by the mass in grams or by a volume in cm^3.
The rate of chemical reaction can be found by measuring the quantity of a reactant used or a product formed over time.