Measure the change in Temperature during Chemical Reactions

   Our Objective

 Measure the temperature change during a chemical reaction to determine whether it is exothermic or endothermic. 

   The Theory

Any chemical reaction results in the formation or breaking of chemical bonds. When chemical bonds form, heat is released, and when they break, heat is absorbed. Because molecules prefer to stay together, creating chemical bonds between them requires less energy than dissolving chemical bonds, which require more energy and releases heat into the environment. Energy changes are a common part of chemical reactions. Energy is absorbed in some reactions while being released as heat in others. Exothermic refers to chemical reactions that release energy. When bonds are formed in the products of exothermic reactions, more energy is released than is required to break the bonds between the reactants. Endothermic refers to chemical reactions that either use or absorb energy. When bonds in the reactants are broken in endothermic reactions, more energy is absorbed than is released when new bonds are formed in the products. An isothermic chemical reaction has no net energy change because it absorbs exactly as much energy as it releases. 

In this experiment the following chemical reactions can be carried out: 

(i) NaOH (aq) + HCl (g) → NaCl (g) + H2O (l) 

(ii) Ba(OH)2.8H2O (s) + 2NH4Cl (s) →BaCl2 (aq) + 10H2O (l) + 2NH3(aq) 


How to Identify Exothermic and Endothermic Reactions

1. By tracking variations in temperature, the temperature of the reaction mixture rises when energy is released in an exothermic reaction. In an endothermic reaction, the temperature drops as energy are absorbed. Placing a thermometer in the reaction mixture will allow you to keep track of temperature changes.

2. By calculation (ΔH) enthalpy of the reaction

The change in heat energy that takes place as reactants transform into products is known as a reaction's enthalpy. If the reaction absorbs heat, H is positive; if it releases heat, H is negative. You can calculate something known as the enthalpy change (H), or heat of reaction, which contrasts the energy of the reactants with the energy of the products, to categorize the net energy output or input of chemical reactions.

An indicator of internal energy is enthalpy. The enthalpy change (H), can be mathematically expressed as: 

 H = energy used in reactant bond-breaking + energy released in product bond-making  

is what is discovered when you calculate the difference between the enthalpy of the products and the enthalpy of the reactants. 

The chemical reaction is exothermic if H is negative (-), as more energy is released during the formation of the products that are used to disintegrate the reactants. The chemical reaction is endothermic if H is positive (+), meaning that less energy is released when the products are created than was required to break down the reactants. Energy changes are a common part of chemical reactions. Energy is absorbed in some reactions while being released as heat in others. 


Respiration is an Exothermic Reaction?

Respiration is an exothermic process because energy is released during the process. During the process, glucose is formed from the food's carbon dioxide. In our cells, this glucose combines with oxygen to produce a significant amount of energy. 

Learning Outcome

  1. Describe how endothermic and exothermic reactions differ.
  2. Define endothermic and exothermic chemical reactions.
  3. Calculate the temperature change experienced during a reaction.