Chemistry 9701 · AS & A Level · The Periodic Table: chemical periodicity

The Periodic Table: chemical periodicity — practice question

G is one compound in the ether family. The structure of G is shown in Fig. 3.1.
(a(i))[1]

The atoms in a CO molecule are joined by a triple covalent bond. One of these bonds is a coordinate (dative covalent) bond. Draw a dot-and-cross diagram to show the outer-electron arrangement in a CO molecule. Use • to represent electrons from an oxygen atom. Use \times to represent electrons from a carbon atom.

(a(ii))[2]

Calculate the bond energy of C≡O from the bond energy values in Table 3.1 and the enthalpy change, $\Delta H$, for the thermal decomposition of G. Show your working. $\text{C}_4\text{H}_{10}\text{O(g)} \rightarrow \text{C}_2\text{H}_6\text{(g)} + \text{CO(g)} + \text{CH}_4\text{(g)} \quad \Delta H = -7.00\,\text{kJ mol}^{-1}$

(a(iii))[2]

When G, $\text{C}_4\text{H}_{10}\text{O}$, is heated in a sealed container, an equilibrium mixture forms. $\text{C}_4\text{H}_{10}\text{O(g)} \rightleftharpoons \text{C}_2\text{H}_6\text{(g)} + \text{CO(g)} + \text{CH}_4\text{(g)}$ Complete the expression for the equilibrium constant, $K_c$, for this reaction. State the units of $K_c$.

(a(iv))[2]

Thermal decomposition of G in the presence of I$_2$ changes the activation energy, $E_a$, for the reaction. Table 3.2 gives $E_a$ for the thermal decomposition of G with and without I$_2$. State the effect of adding I$_2$ to the reaction mixture on the value of $K_c$. Explain your answer.

(a(v))[2]

Fig. 3.2 shows the Boltzmann distribution of energies for molecules of G at constant temperature, $T\,^{\circ}\text{C}$. Sketch, on Fig. 3.2, the Boltzmann distribution of energies for molecules of G at a higher temperature, $(T + 100)\,^{\circ}\text{C}$.

(iii)[2]

When G, $\text{C}_4\text{H}_{10}\text{O}$, is heated in a sealed container, an equilibrium mixture forms. $\text{C}_4\text{H}_{10}\text{O}(g) \rightleftharpoons \text{C}_2\text{H}_6(g) + \text{CO}(g) + \text{CH}_4(g)$ Complete the expression for the equilibrium constant, $K_c$, for this reaction. State the units of $K_c$.

(iv)[2]

The thermal decomposition of G in the presence of $\text{I}_2$ changes the activation energy, $E_a$, for the reaction. Table 3.2 shows $E_a$ for the thermal decomposition of G with and without $\text{I}_2$. State the effect of adding $\text{I}_2$ to the reaction mixture on the value of $K_c$. Explain your answer.

(v)[2]

Fig. 3.2 shows the Boltzmann distribution of energies for molecules of G at constant temperature, $T\degree\text{C}$. Sketch, on Fig. 3.2, the Boltzmann distribution of energies for molecules of G at a higher temperature, $(T + 100)\degree\text{C}$.

(b(i))[1]

Identify the type of structural isomerism shown between G and H using the information in Table 3.3.

(b(ii))[1]

Identify the type of structural isomerism shown between H and J using the information in Table 3.3.

(b(iii))[3]

Draw a possible structure for H and for J. State the systematic name for each structure.

(c)[2]

K has molecular formula $\text{C}_3\text{H}_6\text{O}$. When K is added to 2,4-dinitrophenylhydrazine, an orange precipitate is formed. When K is warmed with Tollens’ reagent, a silver mirror is formed. Draw the displayed formula of K.

Worked solution & mark scheme

This 22-mark question has a full step-by-step worked solution and mark scheme. One marking point: accurate dot-and-cross diagram for CO

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