Specific heat, which is also known as thermal capacity, is the amount of heat required to raise the temperature of one gram of substance by 1∘. To compute specific heat, you would use the equation:
Q = cm Δt, where Q is the amount of heat added, c is the specific heat, m is the mass of the substance, and Δt is the temperature change.
From this equation, we can see why different substances have different specific heats. Each substance will have a different mass, so when the amount of heat and the change in temperature are held constant, the only variable is the mass. Therefore, because mass is the only variable, so because substances have different masses, they will have different specific heats.