Chem 1000: Heats of Reaction & Calorimetry

Another type of energy that contributes to the internal energy of a system is CHEMICAL ENERGY which is associated with chemical bonds and intermolecular attractions.

A HEAT OF REACTION, qrxn, is the quantity of heat exchanged between a system and its surroundings when a chemical reaction occurs at a constant temperature.

• If the reaction occurs in an isolated system, the reaction produces a change in the thermal energy of the system-the temperature either increases or decreases

There are two types of heats of reactions which are:

• Exothermic reaction : Produces a temperature increase in an isolated system or non-isolated system, gives off heat to the surroundings. The heat of reaction for exothermic reaction is negative (qrxn <0)
• Endothermic reaction: Produces a temperature decrease in an isolated system or a gain of heat from the surroundings by a non isolated system. The heat of reaction for endothermic reaction is positive (qrxn > 0)

Heats of reaction are determined in a calorimeter, a device for measuring quantities of heat.

BOMB CALORIMETER

The equation used to represent the qrxn in a calorimeter is:

q_rxn= - q_calorim (where q_calorim= q_bomb + q_water)

We can define the heat capacity of the calorimeter as :

 q_calorim= heat capacity of calorim x change in temperature