F325: Module 1: Equilibria
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What is the equilibrium constant?
Kc=[products]/[reactants] (raised to the power of the moles that they appear as in the equation)
What is a dynamic equilibrium? What must a system be in order for it to be in a dynamic equilibrium.
.A dynamic equilibrium is when the rate of the forward reaction and backward reaction are occurring at the same rate. When this is happening, the macroscopic properties eg. temperature, pressure, concentration, mass and volume remain constant. A system must be closed for dynamic equilibrium to occur.
What is le Chatelier’s principle?
If a change is applied to a system in equilibrium, the equilibrium will shift to minimise the effect of the change.
In the reaction of iodine gas with hydrogen gas, how may Kc be calculated?
• The concentration may be calculated using a colorimeter (because iodine gas is purple) • Concentration of other species can be calculated using the balanced chemical equation (stoichiometry) and from knowing how much of each reactant you started with. • Kc may be calculated by substituting the concentrations into the Kc expression.
Describe the contact process for the manufacture of sulphuric acid.
1 mole of sulphur dioxide reacts with one mole of oxygen from the air to produce sulphur trioxide. -V2O5 catalyst -1/2 atmospheres -400/450 degrees Celsius Sulphur trioxide dissolved in conc sulphuric acid Reacted with water to make twice as much sulphuric acid as you used.
What does a high value of Kc indicate?
A high percentage of products compared to reactants
What happens to the value of Kc if you increase the temperature? What happens to the value of Kc if you increase the pressure?
Kc increases if the forward reaction is endothermic. Kc decreases if the forward reaction is exothermic. Pressure has no effect on the value of Kc.
How does a change in • concentration • pressure • catalyst affect the value of Kc
Nothing other than temperature affects the value of Kc.