(3) change only if some internal factor changes Explanation: In economics, economic equilibrium is a state of the world where economic forces are balanced and in the absence of external influences the (equilibrium) values of economic variables will not change. For example, in the standard text-book model of perfect competition, equilibrium occurs at the point, at which quantity demanded and quantity supplied is equal. Equilibrium can change if there is a change in demand or supply conditions which arc internal factor changes.