Unit 3.1
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Explain why controlling the rate of a chemical reaction is important in the chemical industry.
If the rate is too slow- not profitable. If the rate is too high - risk of explosion.
Explain why energy is required in a chemical reaction.
To break the chemical bonds.
State the two conditions required for successful collisions to take place during a chemical reaction.
The required energy to break the bonds - activation energy. The correct angle of collision.
State the meaning of the term activation energy.
The minimum energy required for successful collisions.
Use ‘Collision Theory’ to explain the effects of concentration, particle size, temperature, and pressure on reaction rate.
If the concentration of a solution is increased or pressure is increased there are more particles in the same volume, particles are closer together which increases the frequency of collisions. If temperature is increased the particles have more energy and therefore collide with each other more often. An increase in temperature also results in more particles having the required activation energy. If the particle size of a solid is decreased the surface area for collisions to occur increases leading to an increase in the frequency of collisions.
State the effect a catalyst has on the activation energy and use this to explain why a catalyst increases rate.
Catalysts lower the activation energy, more particles now have the required activation energy.
Define temperature in terms of the kinetic energy of particles in a substance.
The temperature of a reaction is a measure of the average kinetic energy of all the particles present.
Explain the effect of increasing or decreasing temperature on rate using an energy distribution diagram.
Add a line to an energy distribution diagram to show how a catalyst affects the activation energy. More particles now have the required energy for successful collisions.
whats relative rate or reaction formula
r=1/t
Define endothermic and exothermic in terms of the energy of reactants and products.
Endothermic- energy is taken in, so products have more energy than reactants. Exothermic - energy is given out, so products have less energy than the reactants.
State the meaning of the term enthalpy change.
The difference in energy between reactants and products.
Work out the activation energy and enthalpy change for both forward and reverse reactions using a potential energy diagram.
Forward reaction Ea = 100 kJmol-1 DH =-100kJmol-1. Reverse reaction Ea = 200kJmol-1 DH = +100kJmol-1.
State the meaning of the term activated complex and identify where it is formed on a potential energy diagram.
An unstable arrangement of atoms formed between reactants and products.
State the effect a catalyst has on the activation energy and enthalpy change.
Lowers Ea, no effect on enthalpy change.
Alter a potential energy diagram to show how a catalyst affects the reaction pathway.
Ep/ kJmol-1.