(i) Draw and label an energy profile diagram of an endothermic reaction. Indicate on your diagram the I. activation energy II. heat change, \(\Delta\)H. (ii...
Question 1 Report
(i) Draw and label an energy profile diagram of an endothermic reaction. Indicate on your diagram the I. activation energy II. heat change, \(\Delta\)H.
(ii) Explain how the rate of reaction is affected by I. addition of a catalyst, II. increase in temperature.
(b)(i) Write an equation for the thermal decomposition of calcium trioxocarbonate (IV)
(ii) Determine the volume of carbon (IV) oxide measured at s.t.p. that would he produced by the thermal decomposition of 10g calcium trioxocarbonate (IV). [ Ca = 40; O = 16; C = 12 ]
(c)(i) Give one use cf each of the following forms of carbon: I. coal; II. wood charcoal; Ill. carbon (IV) oxide.
(ii) Write a balanced chemical equation to show what happens when each of the following compounds is heated strongly: I. NaNO\(_{3(s)}\) II. MgCO\(_{3(s)}\).
(d) Consider the following compounds: CaO, CaCO\(_3\), Ca(OH)\(_2\), NaOH Which of them is
(i) used in the manufacture of cement;
(ii) used to detect the presence of carbon (IV) oxide;
(iii) used to liberate carbon (IV) oxide when dilute acid is added;
(iv) hygroscopic;
(v) deliquescent?
Answer Details
(a)(i) Energy profile diagram for an endothermic reaction
In an endothermic reaction, the products have more energy than the reactants. Therefore, the heat change, \(\Delta H\), is positive. The activation energy, \(E_a\), is the energy difference between the reactants and the highest point on the energy profile.
(a)(ii) Effect on the rate of reaction
- Addition of a catalyst: A catalyst provides an alternative reaction pathway with a lower activation energy. More collisions then have enough energy to react, so the reaction rate increases.
- Increase in temperature: Particles gain kinetic energy. They move faster, collide more often, and a greater proportion of collisions have energy equal to or greater than the activation energy. The reaction rate therefore increases.
(b)(i) Thermal decomposition of calcium trioxocarbonate(IV)
\[ \mathrm{CaCO_{3(s)} \rightarrow CaO_{(s)} + CO_{2(g)}} \]
(b)(ii) Volume of carbon(IV) oxide produced at s.t.p.
\[ M_r(\mathrm{CaCO_3}) = 40 + 12 + (3 \times 16) = 100 \]
\[ \text{Moles of } \mathrm{CaCO_3} = \frac{10\text{ g}}{100\text{ g mol}^{-1}} = 0.10\text{ mol} \]
From the balanced equation, \(1\) mole of \(\mathrm{CaCO_3}\) produces \(1\) mole of \(\mathrm{CO_2}\). Therefore, \(0.10\) mole of \(\mathrm{CO_2}\) is produced.
At s.t.p., \(1\) mole of gas occupies \(22.4\text{ dm}^3\).
\[ \text{Volume of } \mathrm{CO_2} = 0.10 \times 22.4 = 2.24\text{ dm}^3 \]
Volume of carbon(IV) oxide produced = \(2.24\text{ dm}^3\).
(c)(i) One use of each form of carbon
- Coal: used as a fuel.
- Wood charcoal: used to absorb poisonous gases.
- Carbon(IV) oxide: used in fire extinguishers.
(c)(ii) Equations for strong heating
\[ \mathrm{2NaNO_{3(s)} \rightarrow 2NaNO_{2(s)} + O_{2(g)}} \]
\[ \mathrm{MgCO_{3(s)} \rightarrow MgO_{(s)} + CO_{2(g)}} \]
(d) Uses and properties of the compounds
| Requirement | Compound | Reason |
|---|---|---|
| Used in the manufacture of cement | \(\mathrm{CaCO_3}\) | Calcium trioxocarbonate(IV), or limestone, is a raw material for cement manufacture. |
| Used to detect carbon(IV) oxide | \(\mathrm{Ca(OH)_2}\) | Limewater turns milky when carbon(IV) oxide is passed through it. |
| Liberates carbon(IV) oxide with dilute acid | \(\mathrm{CaCO_3}\) | Carbonates react with acids to produce carbon(IV) oxide. |
| Hygroscopic | \(\mathrm{CaO}\) | Calcium oxide absorbs moisture from the air. |
| Deliquescent | \(\mathrm{NaOH}\) | Sodium hydroxide absorbs water vapour until it dissolves in the absorbed water. |
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