The following reaction is exothermic: c2h4(g)+br2(g)⇌c2h4br2(g)part apredict the effect on the reaction (shift right, shift left, or no effect) of the following changes.
a) increasing the reaction temperature. b) decreasing the reaction temperature.

a) reaction will go in backward direction (towards left)

b)  reaction will go in forward direction (towards right)

Explanation:

According to Le Chatelier's Principle, the change in any state of the equilibrium say temperature, volume, pressure, or the concentration, the equilibrium will oppose these changes and will shift in such a way that the effect cause must be nullified.

For an exothermic reaction,

On increasing the temperature, reaction will go in backward direction (towards left), because according to Le Chatelier's principle as we increase the temperature,  the equilibrium is will be disturbed , so to again establish the equilibrium, the temperature need to be reduced , hence , the reaction will go in backward direction (towards left).

On decreasing the temperature, reaction will go in forward direction (towards right), because according to Le Chatelier's principle as we decrease the temperature,  the equilibrium is will be disturbed , so to again establish the equilibrium, the temperature need to be increased , hence , the reaction will go in forward direction (towards right).