How do you calculate the heat liberated in joules (J)?
Heat is liberated when an exothermic reaction takes place or when latent heat is released (during a phase change). The heat released during a chemical reaction can be measured by an increase in temperature, while the heat released during a phase change (say water to ice) can be calculated by knowing the latent heat. For a given exothermic reaction, heat released is given as:
q = mC(deltaT)
Heat released = mass x specific heat capacity x temperature change
If the mass is measured in grams, specific heat capacity is measured in joules per gram per degree Celsius and the temperature is measured in degrees Celsius, then the heat released will have the units of joules or J.
Similarly, given the latent heat of transformation and mass of the substance, we can calculate the heat liberated in joules by multiplying the two values together.
Hope this helps.