Enthalpy Change and Calorimetry

This video tutorial explains how to determine the standard enthalpy change of combustion through an experiment using ethanol as a fuel. It covers the setup and procedure of the experiment, including measuring the temperature change of water to calculate thermal energy. The video also discusses potential reasons for discrepancies between experimental and published values, such as heat loss and incomplete combustion.

What is the standard enthalpy change of combustion?

• The energy change when one mole of a substance reacts with oxygen under standard conditions.

• The energy change when one mole of a substance is dissolved in water.

• The energy change when one mole of a substance is formed from its elements.

• The energy change when one mole of a substance is vaporized.

What is the purpose of using a calorimeter in the experiment?

• To measure the mass of the fuel.

• To measure the pressure of the reaction.

• To contain the water and measure its temperature change.

• To ignite the fuel.

Why is it important to cap the spirit burner when not in use?

• To prevent the calorimeter from overheating.

• To ensure complete combustion.

• To increase the temperature of the water.

• To prevent the fuel from evaporating.

How is the thermal energy transferred to the water calculated?

• By measuring the volume of water used.

• Using the equation q = m ΔH.

• By measuring the mass of the fuel burned.

• Using the equation q = m c ΔT.

What is the specific heat capacity of water used in the calculations?

• 3.18 J/g°C

• 4.18 J/g°C

• 2.18 J/g°C

• 5.18 J/g°C

How is the number of moles of ethanol combusted calculated?

• By multiplying the volume of ethanol by its density.

• By dividing the volume of ethanol by its density.

• By multiplying the mass of ethanol by its molar mass.

• By dividing the mass of ethanol by its molar mass.

What is the calculated standard enthalpy change of combustion for ethanol in the experiment?

• -1000 kJ/mol

• -500 kJ/mol

• -1367 kJ/mol

• -748.8 kJ/mol

Why might the experimental value of enthalpy change differ from the published value?

• Use of a different fuel.

• Incorrect measurement of water temperature.

• Incorrect calculation of moles.

• Evaporation of fuel, heat loss to surroundings, incomplete combustion.

What happens if the spirit burner is left uncapped?

• The reaction becomes endothermic.

• The calorimeter becomes too hot.

• The water temperature decreases.

• The fuel evaporates, leading to inaccurate results.

What is one reason for heat loss in the experiment?

• Heat is absorbed by the balance.

• Heat is lost through the spirit burner.

• Heat is absorbed by the thermometer.

• Heat is transferred to the metal calorimeter and the air.