1.1 Controlling the Rate Flashcards
Explain why controlling the rate of a chemical reaction in an industrial process is important.
If the rate is too low then the process will not be economically viable. If it is too high there will be a risk of thermal explosion.
Using collision theory, explain the effect of concentration on the rate of reaction.
By increasing the concentration we increase the number of acid particles in a given volume. This leads to more collisions between the acid and the marble per second. More of the collisions will have sufficient energy and correct orientation for a reaction to occur so the number of effective collisions increases, hence the rate increases.
Using collision theory, explain the effect of particle size on the rate of reaction.
By decreasing the particle size, the surface area in contact with the acid increases. This increases the number collisions per second. More collisions will have sufficient energy and be in the correct orientation so the rate of reaction will increase.
Using collision theory, explain the effect of temperature on the rate of reaction.
If we increase the temperature of the reaction, we increase the speed of the
particles. Particles moving at a greater speed result in more successful collisions, therefore increased rate of reaction. An increase in temperature means more particles have energy equal to or greater than the activation energy.
Using collision theory, explain the effect of pressure on the rate of reaction.
The higher pressure in a gaseous reaction the closer together the particles. This leads to an increase in the number of collisions between the reactant gas molecules so increases the number of collisions with sufficient energy and correct orientation. Hence the rate of reaction increases.
By using collision theory, explain the effect collision geometry has on the rate of reaction.
For a successful collision to take place, the collision geometry must be right, meaning the particles must be in the correct orientation. This means that the activated complex can be formed.
State the units of relative rate.
s⁻¹
Define enthalpy change.
The enthalpy change is the energy difference between the products and the reactants.
State the sign for the enthalpy change for an endothermic reaction.
The enthalpy change is positive in an endothermic reaction.
State the sign for the enthalpy change for an exothermic reaction.
The enthalpy change is negative in an exothermic reaction.
Define activation energy in terms of the formation of an activated complex.
The activation energy is the minimum kinetic energy required by colliding particles to form an activated complex.
Describe an activated complex.
An activated complex is an unstable arrangement of atoms formed at the maximum of the potential energy barrier, during a reaction.
What is a catalyst?
A catalyst is a substance that increases the rate of reaction but can be recovered unchanged at the end of the reaction.
Explain how a catalyst increases the rate of reaction.
A catalyst provides an alternative reaction pathway with a lower activation energy. By reducing the activation energy the catalyst allows more reactant molecules to have an energy greater than the activation energy so increases the rate of reaction.
What is temperature?
Temperature is a measure of the average kinetic energy of the particles in a substance.
