physical science/control test 7 nw/september 2020\nquestion 4\nconsider the decomposition reaction of…

physical science/control test 7 nw/september 2020\nquestion 4\nconsider the decomposition reaction of dinitrogen pentoxide:\n2 n₂o₅(g) → 2 n₂o₄(g) + o₂(g)\nthe table below shows the different energies for the above reaction.\n| heat the of reactants (hᵣ) | 26.6 kj mol⁻¹ |\n| activation energy (eₐ) | 6.73 kj mol⁻¹ |\n| heat of the reaction (δh) | -7.28 kj mol⁻¹ |\n4.1 define the term activation energy.\n4.2 is the above reaction endothermic or exothermic? give a reason for the answer.\n4.3 calculate the heat of the products.\n4.4 draw the potential energy versus course of reaction graph for the above reaction.\non the graph indicate values for:\n- heat of reactants (h reactants)\n- heat of products (h products)\n- energy at the activated complex\n- heat of the reaction (δh)\n4.5 on the same graph drawn in question 4.4, use a dotted line and draw the shape of the graph when a catalyst is added to the original reaction.

physical science/control test 7 nw/september 2020\nquestion 4\nconsider the decomposition reaction of dinitrogen pentoxide:\n2 n₂o₅(g) → 2 n₂o₄(g) + o₂(g)\nthe table below shows the different energies for the above reaction.\n| heat the of reactants (hᵣ) | 26.6 kj mol⁻¹ |\n| activation energy (eₐ) | 6.73 kj mol⁻¹ |\n| heat of the reaction (δh) | -7.28 kj mol⁻¹ |\n4.1 define the term activation energy.\n4.2 is the above reaction endothermic or exothermic? give a reason for the answer.\n4.3 calculate the heat of the products.\n4.4 draw the potential energy versus course of reaction graph for the above reaction.\non the graph indicate values for:\n- heat of reactants (h reactants)\n- heat of products (h products)\n- energy at the activated complex\n- heat of the reaction (δh)\n4.5 on the same graph drawn in question 4.4, use a dotted line and draw the shape of the graph when a catalyst is added to the original reaction.

Answer

Explanation:

4.1

Activation energy is the minimum amount of energy that reactant molecules must possess in order to undergo a chemical reaction.

4.2

Step1: Analyze heat of reaction value

The heat of the reaction $\Delta H=- 7.28\ kJ\ mol^{-1}$. Since $\Delta H < 0$, the reaction is exothermic.

Step2: State the reason

In an exothermic reaction, the products have less energy than the reactants, and heat is released to the surroundings.

4.3

Step1: Recall the formula

The formula for the heat of the reaction is $\Delta H=H_{products}-H_{reactants}$.

Step2: Rearrange the formula to solve for $H_{products}$

$H_{products}=\Delta H + H_{reactants}$.

Step3: Substitute the given values

$H_{reactants}=26.6\ kJ\ mol^{-1}$ and $\Delta H=-7.28\ kJ\ mol^{-1}$. So $H_{products}=-7.28 + 26.6=19.32\ kJ\ mol^{-1}$.

4.4

When drawing the potential - energy versus course of reaction graph:

  • Mark the heat of reactants ($H_{reactants}=26.6\ kJ\ mol^{-1}$) on the y - axis at the start of the reaction.
  • The heat of products ($H_{products}=19.32\ kJ\ mol^{-1}$) is marked on the y - axis at the end of the reaction.
  • The activation energy ($E_a = 6.73\ kJ\ mol^{-1}$) is the energy difference between the reactants and the activated complex. The energy of the activated complex is $26.6 + 6.73=33.33\ kJ\ mol^{-1}$. Draw a curve starting from the reactants, rising to the activated complex and then falling to the products.

4.5

When a catalyst is added:

  • A catalyst lowers the activation energy of the reaction. On the same graph, draw a dotted - line curve that starts and ends at the same points as the original curve (representing the reactants and products), but has a lower peak (lower activation energy).

Answer:

4.1: Activation energy is the minimum energy required for reactant molecules to react. 4.2: Exothermic. Reason: $\Delta H=-7.28\ kJ\ mol^{-1}<0$, heat is released. 4.3: $19.32\ kJ\ mol^{-1}$ 4.4: Graph with $H_{reactants}=26.6\ kJ\ mol^{-1}$, $H_{products}=19.32\ kJ\ mol^{-1}$, energy of activated complex $33.33\ kJ\ mol^{-1}$. 4.5: Dotted - line curve on the same graph with lower activation energy.