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The rate of chemical reactions is affected by changes in temperature and pressure.
(a) (i) Draw a curve on the axes to show the Boltzmann distribution of energy of particles in a sample of gaseous krypton atoms at a given temperature.
Label the curve T1 and label the axes.
[2]
(ii) On the diagram in (a)(i), draw a second curve to show the distribution of energies of the krypton atoms at a higher temperature.
Label the second curve T2.
[1]
(b) The Boltzmann distribution assumes that the particles behave as an ideal gas.
(i) State two assumptions of the kinetic theory as applied to an ideal gas.
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[2]
(ii) 2.00 g of krypton gas, Kr(g), is placed in a sealed 5.00 dm^3 container at 120 °C.
Calculate the pressure, in Pa, of Kr(g) in the container.
Assume Kr(g) behaves as an ideal gas.
Show your working.
pressure = ......................................... Pa [3]
(iii) State and explain the conditions at which krypton behaves most like an ideal gas.
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[2]
(c) Krypton reacts with fluorine in the presence of ultraviolet light to make krypton difluoride, KrF_2(g).
$$\text{Kr(g) + F}_2(\text{g}) \to \text{KrF}_2(\text{g})$$
activation energy for the reaction, $E_a = +385 \text{kJ mol}^{-1}$
enthalpy change of formation of KrF2, $\Delta H_f = +60.2 \text{kJ mol}^{-1}$
(i) Use this information to complete the reaction profile diagram for the formation of KrF2.
Label $E_a$ and $\Delta H_f$ on the diagram.
Assume the reaction proceeds in one step.
[2]
(ii) Explain, in terms of activation energy, $E_a$, and the collision of particles, how an increase in temperature affects the rate of a chemical reaction.
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[2]
577
523
563
Chlorine, $Cl_2$, is a reactive yellow-green gas. It is a strong oxidising agent.
(a) State how $Cl_2$ is used in water purification.
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(b) Chlorine has the highest first ionisation energy of the Period 3 elements Na to $Cl$.
(i) Construct an equation for the first ionisation energy of chlorine.
Include state symbols.
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(ii) Explain the general increase in the first ionisation energies of the Period 3 elements.
................................................................................................................................. [2]
(c) The halide ions, $X^-$ (where $X$ = $Cl, Br, I$), show clear trends in their physical and chemical properties.
(i) State and explain the relative thermal stabilities of the hydrogen halides, $HX$.
................................................................................................................................. [2]
The halide ions react easily with concentrated $H_2SO_4$.
The main sulfur-containing product of each reaction is shown in the table.
| halide ion | $Cl^-$ | $Br^-$ | $I^-$ |
|---|---|---|---|
| main sulfur-containing product of reaction with concentrated $H_2SO_4$ | $HSO_4^-$ | $SO_2$ | $H_2S$ |
| oxidation number of sulfur |
(ii) Complete the table to show the oxidation number of sulfur in each of the sulfur-containing products. [1]
(iii) Explain why different sulfur-containing products are produced when each of these halide ions reacts with concentrated $H_2SO_4$.
................................................................................................................................. [1]
(d) $Cl_2$ reacts with aqueous sodium hydroxide in a disproportionation reaction.
(i) State what is meant by disproportionation.
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(ii) Write an equation for the reaction of $Cl_2$ with cold aqueous sodium hydroxide.
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(e) Aluminium reacts with chlorine to form aluminium chloride.
Aluminium chloride can exist as the gaseous molecule $Al_2Cl_6(g)$. This molecule contains coordinate bonds.
(i) Draw a diagram that clearly shows all the types of bond present in $Al_2Cl_6(g)$.
[2]
(ii) Describe what you would see when solid aluminium chloride reacts with water.
Name the type of reaction that occurs.
................................................................................................................................. [2]
(f) $0.020 ext{ mol of element } Z$ reacts with excess $Cl_2$ to form $0.020 ext{ mol of a liquid chloride}$.
The liquid chloride has formula $ZCl_n$, where $n$ is an integer.
$ZCl_n$ reacts vigorously with water at room temperature to give an acidic solution and a white solid.
When excess $AgNO_3(aq)$ is added to the solution, $11.54 ext{ g of } AgCl(s)$ forms.
(i) Suggest the type of bonding and structure shown by $ZCl_n$.
................................................................................................................................. [1]
(ii) Calculate the value of $n$ in $ZCl_n$.
$n =$ ................................................. [2]
(g) Dichloromethane, $CH_2Cl_2$, is widely used as an organic solvent.
$CH_2Cl_2$ can be prepared by reacting $CH_3Cl$ and $Cl_2$ at room temperature.
The reaction proceeds via several steps, as shown.
$$\text{initiation: } \quad Cl_2 \rightarrow 2Cl^\bullet$$
$$\text{propagation 1: } \quad Cl^\bullet + CH_3Cl \rightarrow HCl + \cdot CH_2Cl$$
$$\text{propagation 2: } \quad Cl_2 + \cdot CH_2Cl \rightarrow \text{products}$$
$$\text{final step: } \quad Cl^\bullet + \cdot CH_2Cl \rightarrow CH_2Cl_2$$
(i) Give the name of the mechanism of this reaction.
................................................................................................................................. [1]
(ii) State the essential condition required for the initiation step to take place.
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(iii) Give the electronic configuration of $Cl^\bullet$.
$1s^2 $ .......................................................... [1]
(iv) Identify the products of the step labelled propagation 2.
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(v) Name the type of reaction shown in the final step.
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(vi) Suggest the identity of another organic molecule that is a product of the reaction of $CH_3Cl$ and $Cl_2$ under the same conditions.
................................................................................................................................. [1]
566
500
513
Compounds P, Q and R have all been found in the atmosphere of one of Saturn’s moons.
P: N≡C—C≡C—C≡C—N
Q: H—C≡C—C≡N
R: 
(a) The equation for the complete combustion of P, C₄N₂(l), is shown.
$$C_4N_2(l) + 4O_2(g) \rightarrow 4CO_2(g) + N_2(g) \quad \Delta H = -2036 \text{ kJ mol}^{-1}$$
(i) The enthalpy change of formation, $\Delta H_f$, of $CO_2(g)$ is $-384 \text{ kJ mol}^{-1}$.
Calculate the enthalpy change of formation, $\Delta H_f$, of P, in kJ mol⁻¹.
$\Delta H_f$ of P = .......................... kJ mol⁻¹ [2]
(ii) One of the products of the complete combustion of P is nitrogen gas, $N_2(g)$.
Explain the lack of reactivity of nitrogen.
.............................................................................................................................. [1]
(b) Q forms when HCN reacts with ethyne, H—C≡C—H.
(i) Ethyne, HCN and Q are all weak Brønsted–Lowry acids.
Explain what is meant by the term weak Brønsted–Lowry acid.
.............................................................................................................................. [2]
(ii) Ethyne, HCN and Q all contain triple bonds between two atoms.
A triple bond consists of one sigma ($\sigma$) and two pi ($\pi$) bonds.
Draw a labelled diagram to show the formation of one pi ($\pi$) bond. [2]
(c) P and Q can be detected in the atmosphere by infrared spectroscopy.
Identify two absorptions, and the bonds that correspond to these absorptions, that will appear in the infrared spectra of both P and Q.
.............................................................................................................................. [2]
(d) The flow chart shows some reactions of R.
(i) Name the type of reaction shown in reaction 1.
.............................................................................................................................. [1]
(ii) Draw the structure of S, the organic product of reaction 2. [1]
(iii) Name T.
.............................................................................................................................. [1]
(iv) T can also be formed by the reaction of $CH_3CH_2CH_2Br$ with ammonia.
State the necessary conditions of this reaction.
.............................................................................................................................. [1]
567
562
506
Hydroxyethanal, HOCH$_2$CHO, has been observed in dust clouds near the centre of our galaxy.
hydroxyethanal
(a) Predict the bond angles labelled x and y in the diagram of hydroxyethanal.
x = ...............°
y = ...............° [2]
(b) Hydroxyethanal reacts separately with 2,4-dinitrophenylhydrazine (2,4-DNPH) and with Tollens’ reagent.
State what you would observe in each reaction.
reaction with 2,4-DNPH ...........................
reaction with Tollens’ reagent ........................ [2]
(c) Hydroxyethanal is converted to ethanedioic acid, (CO$_2$H)$_2$, when it reacts with excess acidified dichromate(VI) ions, Cr$_2$O$_7^{2-}$.
(i) State the role of acidified Cr$_2$O$_7^{2-}$ in this reaction.
....................................................... [1]
(ii) State and explain any other necessary conditions for this reaction to be successful.
....................................................... [2]
(d) Hydroxyethanal can be reduced to ethane-1,2-diol, (CH$_2$OH)$_2$, as shown.
(i) Write an equation for the reduction of hydroxyethanal to (CH$_2$OH)$_2$.
Use [H] to represent an atom of hydrogen from the reducing agent.
....................................................... [1]
(ii) Identify a reagent for this reduction reaction.
....................................................... [1]
(iii) (CH$_2$OH)$_2$ also forms when an alkene A reacts with cold, dilute, acidified manganate(VII) ions.
Name A.
....................................................... [1]
[Total: 10]
549
543
583
