Chapter 10 - Equilibrium and reaction rates Flashcards
What is the collision theory?
Collision theory is a model that explains why changes in the concentration or energy of reactants may alter the rate of reaction.
What does the collision theory state a reaction needs to occur?
The reactant particles must collide.
The reactant particles must have a minimum amount of energy (the activation energy).
The reactant particles must collide in the correct orientation.
What can to happen with reactant particles increase the rate of reaction?
The frequency of collisions between the reactant particles can be increased.
The energy of the reactant particles can be increased.
The reactant particles can be held in the correct orientation.
How can you increase the frequency of collisions in a solution?
For a reactant in solution, increasing the concentration of the solution increases the number of dissolved particles and so increases the frequency of collisions.
How can the frequency of collisions be increased for a gas reactant?
For a gas reactant, increasing its pressure increases the number of gas particles and so increases the frequency of collisions.
How can the frequency of collisions for a solid reactant?
For a solid reactant, increasing its surface area increases the number of solid particles available to react and so increases the frequency of collisions.
How could you increase the rate of reaction without a catalyst for this reaction:
Cu + S —> CuS
Powder the solids
How could you increase the rate of reaction for this reaction:
Zn + CuSO4 —> ZnSO4 + Cu
Increase the concentration of the copper sulphate solution.
How would you increase the rate of reaction (without using a catalyst) for this reaction:
H2 + Cl2 —> 2HCl
Increase the pressure of the gases
How would you increase the rate of reaction without using a catalyst for this reaction:
CaCO3 + 2HCl —> CaCl2 + H2O + CO2
Increase the temperature of the acid
Magnesium ribbon reacts with dilute hydrochloric acid. State and explain three ways to increase the rate of reaction. (6 marks)
Increase concentration of acid, more frequent collisions of particles in solution with magnesium.
Increase temperature of the acid, greater proportion of the collisions between particles will have the activation energy and be successful.
Use magnesium powder, larger surface area means more frequent collisions between particles in solution and surface.
What is the rate of reaction?
The rate of reaction is the change in the quantity of a reactant or a product divided by the time taken.
How can the physical quantity of any reactant or product be measured?
This could be the change in mass, the concentration of a solution or the volume of a gas.
What happens to the quantity of reactants as the reaction proceeds?
The quantity of reactants fall
What does the stoichiometric ratio in the equation show?
The relative amounts by which the quantities change.
How do you calculate the initial rate of reaction on a graph showing quantity and time.
The initial rate is the gradient of a tangent (change in y/ change in x)
What does the Boltzmann distribution show?
It shows the distribution of kinetic energy among particles (in a gas).
Which particles are able to react when they collide?
Only the particles with enough energy (Ea) - the activation energy, will be able to react when they collide, this will only be a small proportion of the particles.
What are on the x and y axis of the Boltzmann distribution?
Kinetic energy is on the x axis and Number of particles is on the y axis
What is a catalyst and what do they do?
A catalyst is a substance which increases the rate of reaction without being used up by the overall reaction. It allows the reaction to proceed via a different route with lower activation energy. Catalysts can be homogeneous or heterogeneous.
What does a catalyst do to reactant particles when they approach the catalyst surface?
Reactants are adsorbed onto the catalyst surface, weakening their bonds.
What is a heterogeneous catalyst and what state are they and their reactants in?
A heterogeneous catalyst is one in a different phase from the reactants. Heterogeneous catalysts are usually solid with reactants that are gases or liquid.
What are homogeneous catalysts?
They are catalysts that are in the same phase as the reactants and completely mixed with them. The reaction is split into two steps.
They’re usually in solution.
What are catalyst properties?
Catalysts aren’t used up, so do not appear in the overall equation.
Catalysts are often transition metals or their compounds.
Why are catalysts used in many industrial reactions?
They lower the temperature required for a suitable rate of reaction.
At a lower temperature, energy demand is reduced.
Less fossil fuel needs to be burnt to release energy so less carbon dioxide is released to the atmosphere.
Manufacturers spend less on energy.
What is dynamic equilibrium?
When the rate of the forward reaction equals the rate of the backward reaction in a closed system.
What happens to the concentration of the reactants and products when equilibrium is reached?
When equilibrium is established the forward reaction and reverse reactions continue but the concentrations of reactants and products no longer change.
Are the concentrations of reactant and product equal at equilibrium?
Not necessarily
What does Le Chatelier’s principle state?
Le Chatelier’s principle states that when any change is made to the conditions of an equilibrium, the position of the equilibrium moves in the direction that minimises the change.
What happens to the position of equilibrium when the temperature is increased.
The position of equilibrium moves in direction that absorbs heat. (endothermic reaction)
What happens to the position of equilibrium when the temperature is decreased.
The position of equilibrium moves in direction that releases heat. (exothermic reaction)
What happens to the position of equilibrium when the pressure is increased.
The position of equilibrium moves in direction that reduces pressure. The direction giving fewer gas molecules.
What happens to the position of equilibrium when the pressure is decreased.
The position of equilibrium moves in direction that increases pressure. The direction giving more gas molecules.
What happens to the position of equilibrium when the concentration increases.
The position of equilibrium moves in direction that reduces concentration. The direction away from added substance.
What happens to the position of equilibrium when the concentration decreases.
The position of equilibrium moves in direction that increases concentration. The direction towards removed substance.
What happens to the position of equilibrium when a catalyst is added or removed?
The position of equilibrium doesn’t change because it increases the rate of the forward and backward reactions equally.
What is meant by the equilibrium constant, Kc?
The equilibrium constant Kc is the ratio of product concentration to reactant concentrations, raised to the appropriate power.
It only varies for a reaction when the temperature is changed.
It indicates whether the position of equilibrium is to the left or right.
What is the expression for equilibrium constant for the reaction aA + bB ⇌ cC + dD
Kc = (C)^c (D)^d / (A)^a (B)^b
C is the concentration of a product.
A is the concentration of a reactant.
The power is the number of moles in the equation.
In industry why does a compromise between yield and rate have to be made?
For an exothermic reaction, a lower temperature gives a higher yield.
A lower temperature would save energy costs.
However, a lower temperature would slow down the forward and backward reaction so it takes longer to reach equilibrium.
A compromise temperature will have to be used.
When does Kc apply to a reaction.
When the reaction has reached equilibrium.
What does a high value of Kc indicate?
If Kc is greater than 1 it indicates a position of equilibrium to the right.
What does a low value of Kc indicate?
If Kc is less than 1 it indicates a position of equilibrium to the left.
