Chemistry – Organic chemistry - Alcohols | e-Consult

Exothermic Reaction: An exothermic reaction is a chemical reaction that releases heat into the surroundings. This means that the products have lower energy than the reactants, and the energy difference is released as heat. The enthalpy change (ΔH) for an exothermic reaction is a negative value.

Experimental Determination of Enthalpy Change:

The enthalpy change of combustion for ethanol can be determined using a calorimeter. A calorimeter is an insulated container designed to minimize heat loss to the surroundings. The following steps are involved:

1. A known volume of water is placed in the calorimeter. The initial temperature of the water is measured.
2. A known mass of ethanol is heated to a known temperature (e.g., room temperature) and then added to the water in the calorimeter.
3. The mixture is stirred and the temperature of the water is monitored until it reaches a maximum value.
4. The final temperature of the water is recorded.

Calculation:

The heat absorbed by the water can be calculated using the formula: q = mcΔT, where:

• q = heat absorbed (in Joules)
• m = mass of water (in kg)
• c = specific heat capacity of water (4200 J/kg°C)
• ΔT = change in temperature (°C)

The heat released by the combustion of ethanol is equal to the heat absorbed by the water (assuming no heat is lost to the surroundings). Therefore, the enthalpy change of combustion (ΔH) can be calculated as:

ΔH = -q / m

Diagram of Apparatus:

The diagram would show a calorimeter (insulated container), a thermometer, a stirrer, and a Bunsen burner with a wire gauze for heating the ethanol. The ethanol would be heated separately and then added to the calorimeter containing the water.