All chemical reactions involve energy changes. Some reactions liberate heat to the surroundings; others absorb heat from the surroundings. The breaking of chemical bonds in reactants and the formation of new ones in the products is the source of these energy changes. Calorimetry is the experimental determination of the amount of heat transferred during a chemical reaction. This measurement is carried out in a device called a calorimeter, which allows all the heat entering or leaving the reaction to be accounted for. This is done by observing the temperature change within the calorimeter as the reaction takes place; if we know how much energy is needed to change the calorimeter’s temperature by a given amount, we can calculate the amount of energy involved in the reaction. The relation between energy and temperature change for the calorimeter or for any other physical object is known as its heat capacity (C), which is the amount of heat energy required to raise the temperature of that object by 1°C (or 1 K). This can be expressed in mathematical terms as: C = q/ΔT where q is the quantity of heat transferred and ΔT is the change in temperature, calculated as ΔT = Tf − Ti. The larger the heat capacity of a body, the larger the amount of heat required to produce a given rise in temperature. The heat capacity of 1 mol of a substance is known as the molar heat capacity. Also, the heat capacity of 1 g of a substance is known as the specific heat . To determine the specific heat of a substance, measure the temperature change, ΔT, that a known mass, m, of a substance undergoes as it gains or loses a known quantity of heat, q. That is: Specific heat (c) = Quantity of heat gained or lost/Mass of substance (in grams)×Temperature change (ΔT) or c = q/m×ΔT The unit of specific heat is J/g-K or J/g°C.
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