Magnesium Heat of Reaction Experiment

Summary

This experiment explores the combustion of magnesium using Hess’s Law to calculate the heat of reaction. By combining reactions with magnesium oxide and magnesium ribbon, the enthalpy changes were determined through both theoretical and experimental methods. Key concepts such as Hess’s Law, enthalpy change calculations, and the heat of formation were applied. The experiment demonstrated reasonably accurate results but acknowledged potential errors such as heat loss to the environment and leftover reactants affecting the data. This practical application of thermochemistry deepens understanding of reaction enthalpies and the importance of careful experimental design.

Takeaways

• 😀 The experiment focuses on applying Hess's Law to a practical scenario involving the combustion of magnesium.
• 😀 Hess's Law states that the enthalpy change of a reaction is the sum of the enthalpy changes of its steps.
• 😀 The equation for heat of reaction is q = mCpΔT, where q is heat, m is mass, Cp is specific heat, and ΔT is the temperature change.
• 😀 The experiment involves mixing hydrochloric acid with magnesium oxide and magnesium ribbon and measuring temperature changes.
• 😀 In the first reaction, the highest temperature recorded was 30.1°C after reacting magnesium oxide with hydrochloric acid.
• 😀 In the second reaction, the highest temperature recorded was 24.6°C after reacting magnesium ribbon with hydrochloric acid.
• 😀 Hess's Law is applied to combine reactions 2, 3, and 4 to derive reaction 1.
• 😀 The theoretical enthalpy of reaction 1 is calculated using heat of formation values and Hess's Law.
• 😀 Experimental enthalpies are calculated by measuring temperature changes during reactions and applying the equation q = mCpΔT.
• 😀 The final experimental enthalpy values are compared to theoretical values, and percent error is calculated to assess accuracy.
• 😀 Potential sources of error include heat loss to the environment due to the simple coffee cup calorimeter and incomplete reaction of the limiting reactant.

Q & A

What is the purpose of this experiment?

The purpose of this experiment is to apply Hess's law to a practical scenario and to utilize thermochemistry applications to draw conclusions about heat reactions.

What does Hess's law state?

Hess's law states that the enthalpy of a reaction is equivalent to the sum of the enthalpies of its individual steps.

What equation is used to calculate the heat of a reaction?

The equation used is q = m * c * ΔT, where q is the heat of reaction, m is the mass of the system, c is the specific heat capacity, and ΔT is the change in temperature.

What were the initial conditions of the first experiment with hydrochloric acid?

In the first experiment, 50 mL of one molar hydrochloric acid was poured into a coffee cup calorimeter, and the initial temperature of the acid was recorded as 20.7°C.

What was the highest temperature recorded in the first experiment?

The highest temperature recorded in the first experiment was 30.1°C.

What was observed in the second experiment involving magnesium ribbon?

In the second experiment, hydrogen gas was released as the reaction occurred, and the highest recorded temperature was 24.6°C.

How is Hess's law applied to reactions 2, 3, and 4?

To apply Hess's law, reactions 2, 3, and 4 are combined to form reaction 1. This involves flipping reaction 2 and adjusting the equations accordingly.

What is the significance of calculating the theoretical enthalpy of reaction 1?

The theoretical enthalpy of reaction 1 is calculated to evaluate the accuracy of the experimental data by comparing it with the experimental enthalpy values.

How is the experimental enthalpy of reaction calculated?

The experimental enthalpy is calculated by determining the temperature change during the experiment, using the equation q = m * c * ΔT, and converting the result to kJ per mole.

What is the source of error in this experiment?

A potential source of error is heat loss to the environment due to the use of a simple coffee cup calorimeter. Additionally, remnants of the limiting reactant, such as magnesium oxide, could lower the experimental enthalpy by overcompensating for the heat released.