Let’s analyze each question step-by-step regarding the dissolution of magnesium sulfate (MgSO4) in water.
Question 2.1 [2 marks] Is the forward reaction exothermic or endothermic? Explain your answer.
Answer: The forward reaction is endothermic. This can be determined from the potential energy graph; if the products (Mg²⁺ (aq) + SO₄²⁻ (aq)) are at a higher potential energy level than the reactants (MgSO₄ (s)), this indicates that energy is absorbed from the surroundings during the dissolution process.
Question 2.2 [5 marks] Provide the label names for all the letters A–D. Be specific with your labels by referring to the forward and the reverse reaction.
Answer: Assuming a typical potential energy graph, we can label the points:
- A: Potential Energy of Reactants (MgSO₄ (s)) - This is the starting energy level of the solid reactant.
- B: Activation Energy (Ea) - This is the peak energy level that must be overcome for the reactants to form products.
- C: Potential Energy of Products (Mg²⁺ (aq) + SO₄²⁻ (aq)) - This is the energy level of the dissolved ions, which is higher than that of the solid reactant in an endothermic reaction.
- D: Reverse Activation Energy - This is the energy barrier for the reverse reaction (from products back to reactants).
Question 2.3 [3 marks] Calculate the value of the enthalpy (Δ𝐻) for the forward reaction.
Answer: The enthalpy change (ΔH) can be calculated by: \[ ΔH = E_{products} - E_{reactants} \] If we assume from the graph, for example, that the energy level of the reactants (A) is 0 kJ/mol and the products (C) indicate an energy level of +100 kJ/mol, then: \[ ΔH = +100 \text{ kJ/mol} - 0 \text{ kJ/mol} = +100 \text{ kJ/mol} \]
Thus, ΔH for the forward reaction would be +100 kJ/mol. (Note: The actual value should be derived from the specific numbers from the graph if they are provided.)
Question 2.4 [2 marks] Define activation energy.
Answer: Activation energy (Ea) is the minimum amount of energy required for reactants to undergo a chemical reaction. It is the energy barrier that must be overcome for the reactants to transition into products.
Question 2.5 [2 marks] Calculate the activation energy of the forward reaction from the graph.
Answer: To calculate the activation energy (Ea) for the forward reaction, we look at the difference between the energy of the reactants and the peak of the energy barrier (point B). Using the same hypothetical numbers, if the energy of the reactants (A) is 0 kJ/mol and the energy at the peak (B) is 50 kJ/mol: \[ Ea = E_{peak} - E_{reactants} \] \[ Ea = 50 \text{ kJ/mol} - 0 \text{ kJ/mol} = 50 \text{ kJ/mol} \] So, the activation energy for the forward reaction would be 50 kJ/mol. (Again, this assumes values for calculation; you will use values from the graph.)
Question 2.6 [2 marks] Explain how a catalyst would affect the activation energy in the reaction.
Answer: A catalyst lowers the activation energy of a chemical reaction, thereby increasing the rate of the reaction. By providing an alternative reaction pathway with a lower energy barrier, a catalyst enables more reactant molecules to have enough energy to overcome the activation energy, facilitating the formation of products more quickly.
Make sure to adapt the values and calculations based on the specific potential energy graph you have for the magnesium sulfate dissolution reaction.
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