Chemistry - Equlibria

Reversible reactions:

• All reversible reactions reach an dynamic equlibrium.

• Its represented by a double arrow and is when the reactants form products and the products form reactants.

What is Dynamic equilibrium:

When the forward and backward reaction happens at the same rate in a closed system. The term dynamic means the forward and backward reactions are occurring simultaneously.

What are two features of dynamic equilibrium?

• The rate of the forward and backward reactions are equal.

• The concentration of reactants and products remains constant.

What is Le Chatelier’s principle used to predict?

How an equilibrium mixture will change if the conditions are altered.

What does Le Chatelier’s principle state?

When a system is subject to change the system will work to alter the change.

What is the effect of increasing temperature on equilibrium?

If temperature is increased the equilibrium will shift to oppose this and move in the endothermic direction to try to reduce the temperature by absorbing heat.

What is the effect of decreasing temperature on equilibrium?

If temperature is decreased the equilibrium will shift to oppose this and move in the exothermic direction to try to increase the temperature by giving out heat.

Exam style question: what effect would increasing temperature have on the yield of ammonia?

Exam level answer:

* if temperature is increased the equilibrium will shift to oppose this and move in the endothermic, backwards direction to try to decrease temperature. The position of equilibrium will shift towards the left, giving a lower yield of ammonia.

Why is the low temperature compromised in ammonia production?

Whilst it gives a higher yield of product it will result in slower rates of reaction.

Effect of pressure on equilibrium

• Increasing pressure will cause the equilibrium to shift towards the side with fewer moles of gas to oppose the change and thereby reduce the pressure.

• Decreasing pressure will cause the equilibrium to shift towards the side with more moles of gas to oppose the change and thereby increase the pressure.

• f the number of moles of gas is the same on both sides of the equation then changing pressure will have no effect on the position of equilibrium.

Why is the pressure used in industry compromised for high pressures?

Increasing pressure may give a higher yield of product and will produce a faster rate. Industrially high pressures are expensive to produce ( high electrical energy costs for pumping the gases to make a high pressure) and the equipment is expensive (to contain the high pressures)

Effect of Concentration on Equilibrium

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Effect of Concentration on Equilibrium

Increasing the concentration of the reactants will favour the reaction that produces the products as more molecules are available to react. It will increase the yield of the products. Likewise decreasing the concentration of products will favour the reaction producing the reactants.

Effect of catalysts on equlibrium:

Does not affect the equilibrium position. allows equilibrium to be reached faster.