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iGCSE Chemistry: Equilibria (Triple)
Terms in this set (24)
Gas particles move at a speed of several hundred metres per second at room temperature. Explain why gases take several minutes to diffuse across a room
Gas particles collide with air particles and move in random directions
State and explain how increasing temperature affects the diffusion of a gas
Gas diffuses quicker because particles have more energy.
What name is given to the movement of gases?
State the expression for calculating % yield.
% yield = (actual amount of products/theoretical amount of products) x 100
Describe the chemical test for water
Add it to anhydrous copper(II) sulfate which will change from white to blue if water is present
What is meant by the term endothermic?
A reaction in which heat energy is taken in (surroundings get colder)
What is meant by the term exothermic?
A reaction in which heat energy is given out (surroundings get hotter)
Explain why experimental values of enthalpy change differ from theoretical values
Heat energy is lost to the surroundings. Not all the reactants are used up.
(Triple only) Draw an energy level diagram for an endothermic reaction and use ΔH to represent the enthalpy change
(Triple only) Draw an energy level diagram for an exothermic reaction and use ΔH to represent the enthalpy change
(Triple only) What does the symbol ΔH mean
enthalpy (energy) change
Explain the effects of increasing the concentration of solutions on the rate of a reaction in terms of particle collision theory
1) more particles in same space 2) more frequent collisions 3) increase rate of reaction
What is a catalyst?
A substance that speeds up a chemical reaction but is chemically unchanged at the end of the reaction
(Triple only) What is meant by the term activation energy?
The minimum energy that the particles in collision must have if a reaction is going to occur
What does the symbol ⇌ mean?
State the observation in the reaction between HCl(g) and NH₃(g)
White solid formed
The addition of water to anhydrous copper sulfate can be used to test for the presence of water. The reaction is reversible. What is the word equation? Describe the colour change.
anhydrous copper sulfate (white) + water ⇌ hydrated copper sulfate (blue)
(Triple only) For a reversible reaction to reach dynamic equilibria, where must the reaction take place?
In a sealed container
(Triple only) State two features of a reaction that is in dynamic equilibrium
1) The rate of the forward reaction is equal to the rate of the backward reaction. 2) There is no overall change in concentrations.
(Triple only) Why a catalyst does not affect the position of equilibrium in a reversible reaction?
If a reversible reaction is in dynamic equilibrium, a catalyst increases the rate of the forward reaction and the rate of the backward reaction by the same amount, so the position of equilibrium is unaffected
(Triple only) What will happen to the equilibrium position when we add a catalyst? Give a reason for your prediction.
A (g) + B (g) ⇋ C (g) + D (g) (+∆H) Equilibrium will not shift in position, because catalyst does not affect the position of equilibrium
(Triple only) What will happen to the equilibrium position when we decrease pressure? Give a reason for your prediction.
A (g) + B (g) ⇋ C (g) (+∆H) Equilibrium will shift to the left, because there are more molecules on the left hand side
(Triple only) What will happen to the equilibrium position when we decrease temperature? Give a reason for your prediction.
A (g) + B (g) ⇋ C (g) + D (g) (+∆H) Equilibrium will shift to the left, because the forward reaction is endothermic
(Triple only) What will happen to the yield of C when the pressure is increased? Give a reason for your prediction.
A (g) + B (g) ⇋ C (g) (+∆H) Increases because there are fewer molecules on the right hand side
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