QUESTIONSHEETS AS Level - Frankly Chemistry OF DISPLACEMENT 16 1 An experiment was carried out to...
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ENERGETICS I AS TOPIC 5 ENTHALPY OF DISPLACEMENT THERMOMETRIC TITRATION ENTHALPY OF FORMATION ENTHALPY OF COMBUSTION BOND DISSOCIATION ENTHALPY HESS’S LAW AND ENTHALPY DIAGRAMS HESS’S LAW CALCULATIONS HESS’S LAW WITH CALORIMETRY HESS’S LAW WITH BOND DISSOCIATION ENTHALPY TEST QUESTION I TEST QUESTION II Questionsheet 1 Questionsheet 2 Questionsheet 3 Questionsheet 4 Questionsheet 5 Questionsheet 6 Questionsheet 7 Questionsheet 8 Questionsheet 9 Questionsheet 10 Questionsheet 11 QUESTIONSHEETS AS Level CHEMISTRY 16 marks 15 marks 12 marks 12 marks 16 marks 20 marks 15 marks 18 marks 15 marks 19 marks 19 marks Curriculum Press – Licence Agreement: Paper copies of the A-Level Chemistry Questionsheets may be copied free of charge by teaching staff or students for use within their school, provided the Photocopy Masters have been purchased by their school. No part of these Questionsheets may be reproduced or transmitted, in any other form or by any other means, without the prior permission of the publisher. All rights are reserved. This license agreement is covered by the laws of England and Wales © Curriculum Press March 2008. ress urriculum C P www.curriculum-press.co.uk Curriculum Press • Bank House • 105 King Street • Wellington • Shropshire • TF1 1NU Authors Trevor Birt John Brockington Donald E Caddy Kevin Frobisher Andrew Jones Andy Shepherd Stuart Barker Adrian Bond Editors John Brockington Stuart Barker
Transcript of QUESTIONSHEETS AS Level - Frankly Chemistry OF DISPLACEMENT 16 1 An experiment was carried out to...
ENERGETICS IAS TOPIC 5
ENTHALPY OF DISPLACEMENT
THERMOMETRIC TITRATION
ENTHALPY OF FORMATION
ENTHALPY OF COMBUSTION
BOND DISSOCIATION ENTHALPY
HESS’S LAW AND ENTHALPY DIAGRAMS
HESS’S LAW CALCULATIONS
HESS’S LAW WITH CALORIMETRY
HESS’S LAW WITH BOND DISSOCIATION ENTHALPY
TEST QUESTION I
TEST QUESTION II
Questionsheet 1
Questionsheet 2
Questionsheet 3
Questionsheet 4
Questionsheet 5
Questionsheet 6
Questionsheet 7
Questionsheet 8
Questionsheet 9
Questionsheet 10
Questionsheet 11
QUESTIONSHEETS AS LevelCHEMISTRY
16 marks
15 marks
12 marks
12 marks
16 marks
20 marks
15 marks
18 marks
15 marks
19 marks
19 marks
Curriculum Press – Licence Agreement:Paper copies of the A-Level Chemistry Questionsheetsmay be copied free of charge by teaching staff or studentsfor use within their school, provided the PhotocopyMasters have been purchased by their school. No part ofthese Questionsheets may be reproduced or transmitted,in any other form or by any other means, without theprior permission of the publisher. All rights are reserved.This license agreement is covered by the laws of Englandand Wales © Curriculum Press March 2008.
ressurriculumCPwww.curriculum-press.co.uk
Curriculum Press • Bank House • 105 King Street • Wellington • Shropshire • TF1 1NU
AuthorsTrevor Birt John BrockingtonDonald E Caddy Kevin FrobisherAndrew Jones Andy Shepherd
Stuart BarkerAdrian BondEditorsJohn BrockingtonStuart Barker
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TOPIC 5 Questionsheet
TOTAL /
AS Level
ENTHALPY OF DISPLACEMENT
16
1
An experiment was carried out to find the enthalpy change for the reaction:
Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
The temperature of 20.0 cm3 of copper sulfate solution (1.0 mol dm-3) in a plastic cup was measured everyminute for 3 minutes. Exactly on the third minute 1.95g of zinc powder was added rapidly and the mixture stirred.The temperature every half-minute was noted for a further 3 minutes.
a) Calculate:(i) the mol copper ion used
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b) Calculate and explain the mol used in the calculation
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c) The following graph was drawn :
(i) Why was the zinc added after 3 minutes?
....................................................................................................................................................................... [1](ii) Explain how the value of the temperature change ?T was derived from the graph
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(iii) Explain why the method in (ii) was necessary
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Tem
pera
ture
(o C
)
3 Time (min)
∆T
(Continued..)
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TOPIC 5 Questionsheet
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AS Level TOPIC 5 Questionsheet 1 Continued
ENTHALPY OF DISPLACEMENT
d) The value of ∆T was derived as 39.5 0C.
(i) Calculate the joules of energy exchange with the surroundings (assuming that 1 cm3 solution requires4.2 J to increase the temperature by 1 0C).
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(ii) Calculate a value for the enthalpy of reaction
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e) If the experiment was repeated using magnesium instead of zinc, how and why would you expect the enthalpyof reaction to compare with your value in d)(ii) ?
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TOPIC 5 Questionsheet
TOTAL /
AS Level
15
THERMOMETRIC TITRATIONa) The following results were obtained from an experiment to determine the heat of neutralisation of an acid
with an alkali:Hydrochloric acid added to 50 cm3 of 2.0 M sodium hydroxide
Volume of acid added / cm3
0.05.0
10.015.020.025.030.035.040.045.050.0
Temperature of mixture / 0C
17.622.026.030.033.435.434.033.031.630.829.6
(i) Plot a graph of temperature against volume of acid added and use the graph to determine the volume ofacid required to neutralise the 50 cm3 of 2.0 M sodium hydroxide.
2
Volume of acid required = ......................................................................................................................... [5] (Continued..)
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AS Level
15
(ii) Calculate the molar concentration of the acid.
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(iii) Calculate the enthalpy of neutralisation of the acid by the alkali. (Take the specific heat capacity ofdilute solutions to be 4.18 J g-1 K-1)
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b) To confirm this result, 40 cm3 of 2 M hydrochloric acid were put into a Thermos flask and its temperaturerecorded.Then 60 cm3
of 2 M sodium hydroxide were added and the temperature rose by 10.4 0C. The flask
was rinsed out and 100 cm3 of water put in together with a small electrical heating coil. The coil supplied 30Joules every second and after 145 seconds the same temperature rise was achieved. Use the electrical data tocalculate the enthalpy of neutralisation of the acid by the alkali.
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THERMOMETRIC TITRATIONTOPIC 5 Questionsheet 2 Continued
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TOPIC 5 Questionsheet
TOTAL /
AS Level
12
3
ENTHALPY OF FORMATION
a) Define standard enthalpy of formation of a compound.
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b) Calculate the standard enthalpy change for the oxidation of ammonia according to the equation:4NH
3(g) + 5O
2(g) → 4NO(g) + 6H
2O(g)
Standard enthalpies of formation are as follows: NH
3(g) = -46 kJ mol-1 NO(g) = +90 kJ mol-1 H
2O(g) = -242 kJ mol-1
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c) Ethyne burns in oxygen according to the equation:2C
2H
2(g) + 5O
2(g) → 4CO
2(g) + 2H
2O(l)
Calculate the standard enthalpy of combustion of this gas given the following standard enthalpies of formation:C
2H
2(g) = + 228 kJ mol-1 CO
2(g) = -394 kJ mol-1 H
2O(l) = -286 kJ mol-1
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d) Calculate the standard enthalpy of formation of magnesium carbonate, using the following information.The standard enthalpy of combustion of magnesium is – 602 kJ mol-1 and that of carbon is – 394 kJ mol-1.The standard enthalpy change for the decomposition of magnesium carbonate in the reaction:
MgCO3(s) → MgO(s) + CO
2(g)
is +100 kJ mol-1.
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TOPIC 5 Questionsheet
TOTAL /
AS Level 4
12
ENTHALPY OF COMBUSTION
a) Define standard enthalpy of combustion of an element or compound.
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b) Given the following data:2C(s) + O
2(g) → 2CO(g); ∆Hθ = - 222 kJ mol-1
2CO(g) + O2(g) → 2CO
2(g); ∆Hθ = - 566 kJ mol-1
what is the standard enthalpy of combustion of carbon?
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c) The standard enthalpy changes for the combustion of decane, octane and ethene are –6778, -5470 and –1411kJ mol-1 respectively. Use these data to calculate the standard enthalpy change for the cracking of decane:C
10H
22(l) → C
8H
18(l) + C
2H
4(g)
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d) In the presence of a nickel catalyst, but-1-ene can be hydrogenated to give butane:CH
2=CHCH
2CH
3(g) + H
2(g) → CH
3CH
2CH
2CH
3(g)
(i) Calculate the molar enthalpy of hydrogenation of but-1-ene, given the following standard enthalpies ofcombustion:
∆Hθc /kJ mol-1
C4H
8(g) - 2718
H2(g) - 286
C4H
10(g) - 2877
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(ii) State, giving a reason, how you would expect the enthalpy of hydrogenation to change if platinum wereto be used as a catalyst instead of nickel.
Expected change .................................................................................................................................... [1]
Reason .......................................................................................................................................................
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TOPIC 5 Questionsheet
TOTAL /
AS Level
16
5
BOND DISSOCIATION ENTHALPY
a) Define the bond dissociation enthalpy of the H⎯H bond.
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b) Distinguish between the bond dissociation enthalpy of the O⎯H bond in water and the mean bond dissociationenthalpy of the O⎯H bond in water.
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c) Arrange the following in increasing order of mean bond dissociation enthalpy:(i) C—C, C=C, C≡C
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(ii) C—Cl, C—Br, C—I
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d) What is the relationship between bond dissociation enthalpy and (i) bond strength, and (ii) bond length?
Bond strength ................................................................................................................................................. [1]
Bond length ................................................................................................................................................... [1]
e) The combustion of propanone is given by the equation:
(g) + 4O2(g) → 3CO
2(g) + 3H
2O(g)
Use the following mean bond dissociation enthalpies (all in kJ mol-1) to calculate the enthalpy change for thisreaction:
C—C 346 C—H 414 C=O 804 O=O 498 O—H 463
[7]
CH3
CH3
C=O
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TOPIC 5 Questionsheet
TOTAL /
AS Level
20
6
HESS’S LAW & ENTHALPY DIAGRAMS
a) State Hess’s law.
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b) (i) Hess’s law is in accordance with the first law of thermodynamics. State this law.
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(ii) Explain why, if Hess’s law were not obeyed, the first law of thermodynamics would be violated.
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c) (i) Write an equation, with state symbols, for the combustion of propane.
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(ii) Sketch an enthalpy diagram for the formation and combustion of propane. (Hint The formation of propaneis exothermic.) Clearly label ‘start’ and ‘finish’ on your diagram, and show two routes from start tofinish.
[6]
(iii) Apply Hess’s law to your diagram in c) (ii) and hence calculate the standard enthalpy of formation ofpropane, given the following standard enthalpies of combustion (all in kJ mol-1):
C(s) = -394 H2(g) = -286 C
3H
8(g) = -2222
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TOPIC 5 Questionsheet
TOTAL /
AS Level
15
7HESS’S LAW CALCULATIONS
In this question you will need the following data.
Molar enthalpy of vaporisation of water = 41.1 kJ mol-1
a) (i) There are two solid allotropes (i.e. crystalline forms) of sulfur, described as ‘rhombic sulfur’and ‘monoclinicsulfur’. Construct an enthalpy diagram or cycle, and apply Hess’s law to it so as to calculate the standardenthalpy change for the conversion of rhombic sulfur to monoclinic sulfur.
[4]
(ii) From your answer to a) (i) state, with reason, which allotrope of sulfur is the more stable under standardconditions.
More stable form ................................................................................................................................... [1]
Reason .................................................................................................................................................. [1]
Standard enthalpy of formation /kJ mol-1
H2O(l) –286
H2S(g) –20.2
Standard enthalpy of combustion/kJ mol-1
S (rhombic) –296.9S (monoclinic) –297.2
(Continued....)
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TOPIC 5 Questionsheet 7 Continued
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HESS’S LAW CALCULATIONSb) Monoclinic sulfur is formed in volcanic regions by reaction between sulfur dioxide and hydrogen sulfide ac-
cording to the equation:SO
2(g) + 2H
2S(g) → 2H
2O(g) + 3S(monoclinic).
Draw an enthalpy diagram or cycle and calculate the standard enthalpy change for this reaction.
[5]c) For the oxidation of sulfur dioxide to sulfur trioxide according to the equation:
2SO2(g) + O
2(g) → 2SO
3(g); ∆Hθ
reaction = -196.2 kJ mol-1.
From an enthalpy diagram or cycle calculate the standard enthalpy of formation of sulfur trioxide from mono-clinic sulfur.
[4]15
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TOPIC 5 Questionsheet
TOTAL /
AS Level
16
8
HESS’S LAW WITH CALORIMETRY
A student poured exactly 50 cm3 of 2 M hydrochloric acid into a polystyrene cup and recorded its temperatureeach minute for three minutes. At 3½ minutes, 0.24 g of magnesium turnings was added. The mixture was stirredand further temperature readings taken until a total time of nine minutes had elapsed. The recorded temperatureswere as follows.
Time / minutes
Temperature / 0C
0 1 2 3 4 5 6 7 8 9
20 19.7 19.5 19.2 43.8 43.0 42.3 41.5 40.8 40.0
a) Plot a graph of temperature against time using these results and hence determine the maximum temperaturechange accompanying the reaction.
(Continued...)Maximum temperature change ..............................................................................................................[5]
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TOPIC 5 Questionsheet
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AS Level
18
HESS’S LAW WITH CALORIMETRYb) Use the value from a) and the data given in the question to calculate the enthalpy change for the reaction.
(Assume the density of all solutions to be 1 g cm-3 and their specific heat capacity to be 4.2 J g-1 K-1)
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c) In a similar experiment, 0.01 mol of magnesium carbonate was added to exactly 50 cm3 of 2 M hydrochloricacid in a polystyrene cup. The maximum temperature rise was 5.2 0C. Calculate the enthalpy change for thereaction.
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d) Write a balanced chemical equation to represent the standard enthalpy of formation for magnesium carbonate.
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e) Given the additional data for the standard enthalpies of formation of H2O(l) and CO
2(g) as –286 and –394 kJ
mol-1 respectively, together with the reactions above, construct an enthalpy cycle or diagram to show how thestandard enthalpy of formation for magnesium carbonate can be calculated.
[4]
f) Apply Hess’s law to the cycle or diagram you have devised and the results from b) and c) to calculate thestandard enthalpy of formation for magnesium carbonate.
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TOPIC 5 Questionsheet 8 Continued
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TOPIC 5 Questionsheet
TOTAL /
AS Level 9
15
HESS’S LAW WITH BOND DISSOCIATION ENTHALPY
Ethanol production in the UK is mainly from the hydration of ethene. In this process, ethene and steam arereacted together at 300 0C and 70 atm pressure in the presence of phosphoric acid, which acts as a catalyst:
CH2=CH
2(g) + H
2O(g) → C
2H
5OH(l)
a) Apply Hess’s law to an enthalpy cycle or diagram to calculate the enthalpy change for this reaction, given thefollowing data:
Standard enthalpy of formation of ethanol = -278 kJ mol-1
C(s) → C(g); ∆H = + 715 kJ mol-1
Mean bond dissociation enthalpies / kJ mol-1:H—H = 436 O O = 496 C C = 612 O—H = 464 C—H = 413
[8]
b) Calculate the enthalpy change for the same reaction, using the following standard enthalpies of combustion:
CH2=CH
2 = –1411 kJ mol-1 CH
3CH
2OH = –1368 kJ mol-1
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c) Why is the value calculated from bond dissociation enthalpies in a) different from that obtained in b)?
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d) For the formation of gaseous ethanol, CH2=CH
2(g) + H
2O(g) → C
2H
5OH(g)
would you expect the enthalpy of reaction to be more negative or less negative than the value for the formationof liquid ethanol? Give your reason.
More or less negative .................................................................................................................................... [1]
Reason ...............................................................................................................................................................
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TOPIC 5 Questionsheet
TOTAL /
AS Level
17
10
TEST QUESTION I
NOTE In this Questionsheet, assume that dilute aqueous solutions have a specific heat capacity of 4.18 J g-1 K-1
and a density of 1.00 g cm-3.
a) (i) Define the term molar enthalpy of solution.
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(ii) When 5.35 g of ammonium chloride was dissolved in 100 g of water, the temperature fell from 20.55 0Cto 17.10 0C. Calculate the molar enthalpy of solution of ammonium chloride.
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(iii) What is the significance of the sign of the value calculated in (ii)?
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b) 50.0 cm3 of 0.5 mol dm-3 NH3(aq) at 20.00 oC. was mixed with 50.0 cm3 0.5 mol dm-3 HCl(aq), also at 20.00 oC.
The temperature of the mixture rose to 23.12 oC. Calculate the molar enthalpy of neutralisation of HCl(aq) byNH
3(aq).
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(Continued..)
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TOPIC 5 Questionsheet
TOTAL /
AS Level 10 Continued
c) (i) Write an equation to represent the formation of 1 mole of solid ammonium chloride from its elements intheir standard states.
....................................................................................................................................................................... [1]
(ii) Use the following data, together with your answers from a) and b), to calculate the molar enthalpy ofsolution of ammonia. Your answer should include an enthalpy cycle or diagram to which Hess’s law isclearly applied.
∆Hθf / kJ mol-1 : NH
3(g) = -43.2 HCl(g) = -92.3 NH
4Cl(s) = -315
Molar enthalpy of solution of HCl(g) = -187 kJ mol-1
Enthalpy cycle or diagram
[5]
Application of Hess’s law
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Molar enthalpy of solution of ammonia
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TEST QUESTION I
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TOPIC 5 Questionsheet
TOTAL /
AS Level
17
11
TEST QUESTION II
(Continued...)
A spirit burner containing ethanol was weighed. 80 cm3 of water was measured into a metal calorimeter and thetemperature measured. The burner was ignited under the calorimeter and extinguished after 5 minutes.
The temperature of the water and the mass of the burner were then immediately measured. The following resultswere obtained:
Mass of spirit burner at start (g) 32.44
Mass of spirit burner after combustion (g) 31.96
Temperature of water at start (oC) 16.4
Temperature of water after combustion (oC) 33.1
a) Calculate(i) the mass of ethanol burned
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(ii) the temperature rise of the water
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TOPIC 5 Questionsheet
TOTAL /
AS Level 11 Continued
19
TEST QUESTION II
b) Assuming 1cm3 of water rises 1oC for 4.2 J energy , calculate(i) the energy exchange with the surroundings (in joules)
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(ii) the energy yield for ethanol in joules per g
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(iii) the enthalpy of combustion for ethanol
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(iv) Explain why it is not possible to state that the answer to (iii) is the‘standard enthalpy of combustion’.
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(v) Give an assumption used when calculating an answer to (i)
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c) If the standard enthalpy of combustion is -1400 kJ mol-1, suggest and explain two reasons for the difference.
Reason 1 ....................................................................................................................................................... [1]
Explanation ......................................................................................................................................................
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Reason 2 ....................................................................................................................................................... [1]
Explanation ......................................................................................................................................................
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