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## 8.4 Chapter Summary (ESCNY)

Presentation: 27V5

• A reaction is reversible when reactants can react to form products, and products can react to form the reactants again.

• A reaction is in chemical equilibrium when the rate of the forward reaction equals the rate of the reverse reaction.

• In an open system energy and matter can enter and leave the system. In a closed system energy can enter and leave the system, but matter cannot.

• The equilibrium constant ($$\text{K}_{\text{c}}$$) relates to the concentration of the reactants and products at equilibrium, and can be calculated using the following expression:

$${K}_{c}=\frac{{\left[C\right]}^{c}{\left[D\right]}^{d}}{{\left[A\right]}^{a}{\left[B\right]}^{b}}$$ where $$\text{aA} + \text{bB}$$ $$\rightleftharpoons$$ $$\text{cC} + \text{dD}$$

A and B are reactants, C and D are products and a, b, c, and d are the coefficients of the respective reactants and products.

• A high $$\text{K}_{\text{c}}$$ value means that the concentration of products at equilibrium is high and the reaction has a high yield of the products. A low $$\text{K}_{\text{c}}$$ value means that the concentration of products at equilibrium is low and the reaction has a low yield of the products.

• Le Chatelier's Principle states that if an external stress (change in pressure, temperature or concentration) is applied to a system in chemical equilibrium, the equilibrium will change in such a way as to reduce the effect of the stress.

• Although a change in temperature, concentration or total pressure will affect the equilibrium position, only temperature will affect the equilibrium constant $$\text{K}_{\text{c}}$$.

• The principles of equilibrium are very important in industrial applications such as the Haber process, so that productivity can be maximised.