What is reaction rate and how is it expressed?

Reaction rate is the speed at which reactants are consumed or products are formed per unit time. It can be expressed as: change in concentration per unit time (-dCA/dt for reactant A), moles reacted per unit volume per unit time, or moles reacted per unit mass of catalyst per unit time (for catalytic reactions). Rate is typically a function of temperature and concentrations of reactants, expressed through rate laws.