9701_w17_qp_21 - revisedeck

1

Ammonia, NH3, is manufactured from nitrogen and hydrogen by the Haber process. N2+ 3H22NH3ΔH = –92 kJ mol–1 Some bond energies are given. N≡N = 944 kJ mol–1 H–H = 436 kJ mol–1 Explain the meaning of the term bond energy. Use the data to calculate a value for the N–H bond energy. You must show your working. N–H bond energy = kJ mol–1 The Haber process is usually carried out at a temperature of approximately 400 °C in the presence of a catalyst. Changing the temperature affects both the rate of production of ammonia and the yield of ammonia. The Boltzmann distribution for a mixture of nitrogen and hydrogen at 400 °C is shown. Ea represents the activation energy for the reaction. proportion of molecules with a given energy molecular energy Ea Using the same axes, sketch a second curve to indicate the Boltzmann distribution at a higher temperature. With reference to the Boltzmann distribution, state and explain the effect of increasing temperature on the rate of production of ammonia. State and explain the effect of increasing temperature on the yield of ammonia. Use Le Chatelier’s principle to explain your answer. At a pressure of 2.00×107 Pa, 1.00 mol of nitrogen, N2, was mixed with 3.00 mol of hydrogen, H2. The final equilibrium mixture formed contained 0.300 mol of ammonia, NH3. Calculate the amounts, in mol, of N2and H2in the equilibrium mixture. N2= mol H2= mol Calculate the partial pressure of ammonia, pNH3, in the equilibrium mixture. Give your answer to three significant figures. pNH3 = Pa In another equilibrium mixture the partial pressures are as shown. substance partial pressure / Pa N22.20 × 106 H29.62 × 105 NH31.40 × 104 Write the expression for the equilibrium constant, Kp, for the production of ammonia from nitrogen and hydrogen. Kp = Calculate the value of Kp for this reaction. State the units. Kp = units = This reaction is repeated with the same starting amounts of nitrogen and hydrogen. The same temperature is used but the container has a smaller volume. State the effects, if any, of this change on the yield of ammonia and on the value of Kp. effect on yield of ammonia effect on value of Kp

7. Equilibria → 7.1. Chemical equilibria: reversible reactions, dynamic equilibrium

8. Reaction kinetics → 8.2. Effect of temperature on reaction rates and the concept of activation energy

Open

2

The elements in the third period, and their compounds, show trends in their physical and chemical properties. A sketch graph of the first ionisation energies of five successive elements in the third period is shown. ionisation energy atomic number P S Al Mg Si Explain why there is a general increase in the first ionisation energy across the third period. Sketch, on the graph, the position of the ionisation energies of the two elements that come before Mg in this sequence. Explain, with reference to electron arrangements, the decreases in first ionisation energy between Mg and Al and between P and S. Mg and Al P and S The chlorides of the elements in the third period behave in different ways when added to water, depending on their structure and bonding. L and M are each a chloride of an element in Period3. A student investigated L and M and their results are given. L is a white crystalline solid with a melting point of 987 K. L dissolves in water to form an approximately neutral solution. Addition of NaOHto an aqueous solution of L produces a white precipitate. M is a liquid with a boiling point of 331 K. M is hydrolysed rapidly by cold water to form a strongly acidic solution, a white solid and white fumes. Identify L and M. Explain any properties and observations described. Give equations where appropriate. L is M is

9. The Periodic Table: chemical periodicity → 9.2. Periodicity of chemical properties of the elements in Period 3

Open

3

Some reactions based on 1-bromobutane, CH3(CH2)3Br, are shown. CH3(CH2)3Br CH3CH2CH=CH2 CH3(CH2)3OH reaction 1 reaction 2 reaction 3 reaction 5 CH3(CH2)3C≡N CH3(CH2)2CHO reaction 4 reaction 6 CH3(CH2)3COOH CH3(CH2)2COOH For each of the reactions state the reagent, the particular conditions required, if any, and the type of reaction. For the type of reaction choose from the list. Each type may be used once, more than once or not at all. Each reaction may be described by more than one type. elimination hydrolysis substitution oxidation addition condensation reaction reagentand conditions typeof reaction Complete the diagram to show the SN2 mechanism of reaction 1. R represents the CH3(CH2)2 group. Include all necessary charges, dipoles, lone pairs and curly arrows. R C Br H H R C O H H H 2-bromo-2-methylpropane is a tertiary halogenoalkane that is a structural isomer of 1-bromobutane. Define the term structural isomer and name the three different types of structural isomerism. definition types of structural isomerism 2-bromo-2-methylpropane is treated with the same reagents as in reaction 1. Methylpropan-2-ol is formed. Identify the mechanism for this reaction. Explain why this reaction proceeds via a different mechanism from that of reaction1. mechanism explanation The product of reaction 2, but-1-ene, does not show stereoisomerism. However, but-1-ene reacts with HCl to form a mixture of structural isomers X and Y. but-1-ene + HCl X (exists as a pair of stereoisomers and is produced in higher yield than Y) Y (does not show stereoisomerism) Explain the meaning of the term stereoisomers. Give two reasons why but-1-ene does not show stereoisomerism. Name X and Y. X Y Name the type of stereoisomerism shown by X. Use the conventional representation to draw the two stereoisomers of X.

15. Halogen compounds → 15.1. Halogenoalkanes

Open