Chemistry 5070 · O Level · Exothermic and endothermic reactions

Exothermic and endothermic reactions — practice question

Phosphorus reacts with hydrogen to make phosphine, $\text{PH}_3$. $2\text{P} + 3\text{H}_2 \rightarrow 2\text{PH}_3$ It is endothermic.
(a)[2]

Finish the energy profile diagram for this reaction. Label reactants, products and $\Delta H$.

(b)[2]

Explain why the reaction is endothermic in terms of bond breaking and bond forming.

(c)[1]

Phosphine reacts with oxygen to form phosphorus(V) oxide, $\text{P}_4\text{O}_{10}$, and water. Complete the equation for this reaction. $\ldots\,\text{PH}_3 + \ldots\,\text{O}_2 \rightarrow \text{P}_4\text{O}_{10} + \ldots\,\text{H}_2\text{O}$

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This 5-mark question has a full step-by-step worked solution and mark scheme. One marking point: “reactants at left, products at right, with the reactant line lower than the product line” …

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