Which statement describes a chemical change

What is the molecular weight of copper

What is a number added in front of a formula in order to balance the equation

The reaction below shows a system in equilibrium. how would a decrease in temperature affect this reaction? a. the rate of formation of the gases would increase. b. the equilibrium of the reaction would shift to the left. c. the equilibrium would shift to cause the gases to sublime into solids. d. the chemicals on the left would quickly form the chemical on the right.