I would like to know since i was taught that all neutralisation reaction is exothermic, but why is sodium carbonate reacting with citric acid an endothermic reaction?
The reaction between sodium carbonate and citric acid is indeed an example of an endothermic reaction, which means that it absorbs heat from its surroundings.
To understand why this specific reaction is endothermic, we need to analyze the chemical equation and the nature of the reactants involved. The reaction can be represented as follows:
3Na2CO3 (s) + 2C6H8O7 (aq) → 6Na3C6H5O7 (aq) + 3H2O (l) + 3CO2 (g)
In this reaction, sodium carbonate (Na2CO3) reacts with citric acid (C6H8O7) to produce sodium citrate (Na3C6H5O7), water (H2O), and carbon dioxide (CO2).
Now, let's break down how this reaction is endothermic:
1. Ionic bonds: Sodium carbonate is an ionic compound, composed of sodium ions (Na+) and carbonate ions (CO3^2-). Similarly, sodium citrate is also an ionic compound. When sodium carbonate and citric acid react, the ionic bonds in sodium carbonate and citric acid need to be broken. Breaking these bonds requires energy.
2. Hydrogen bond disruption: Citric acid is a polar molecule with multiple functional groups, including three carboxylic acid groups (COOH) and an alcohol group (OH). These functional groups can form hydrogen bonds with water molecules. During the reaction, water molecules are produced, and the hydrogen bonds between the citric acid molecules and water molecules are broken. Breaking hydrogen bonds also requires energy.
3. Gas formation: The production of carbon dioxide gas (CO2) during this reaction contributes to its endothermic nature. The formation of CO2 requires the breaking of bonds within the carbonate ion. This bond-breaking process absorbs energy.
Overall, the breaking of ionic and hydrogen bonds, as well as the formation of CO2, requires energy, making the reaction between sodium carbonate and citric acid endothermic. Keep in mind that not all neutralization reactions are exothermic; there are specific cases like this one where the reaction is endothermic due to the nature of the reactants involved.