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96 Theme 3 I Chemistry of Reoctions
For each of the questions, there are four possible choices.Choose the one you consider coruect and record your choice.
d Which of the following is true when an exothermic reaction
occurs?
A The surroundings gets cooler.
B The enthalpy change for the reaction is positive.
C The products are at a lower energy level than thereactants.
D The energy change for bond breaking is greater than theenergy change for bond forming. ( )
d2. The diagram below shows the conversions between the threestates of water.
2""'\r'\water i-+ ice
d
d
Which of the following conversions are endothermic?
I lce - Steam
ll Water * lce
lll Steam - WaterlV lce - Water
A I and ll only B I and lV only
C ll and lll only D lll and lV only (
3. Which of the following is an exothermic process?
A lVelting of rce
B Evaporation of ethanol
C Formation of iodine vapour from iodine crystalsD Condensation of water vapour t0 form liquid droplets
(
4. Dissolving solid calcium chloride in water is an exothermicprocess. Which of the following graphs shows the temperature
changes as the solid is added to water, stined and the solution
left to stand?
A remperature
temperatureroom
0
B
temperature
roomtemperature
Temperature
TemperatureC
Time
Time0
Temperature
roomtemperature
Time
5. Below is an energy profile diagram for a chemical reactionshowrng the energy changes l, ll, lll and lV
products
D
d
III
tI
IV
IIII
I
Time
0
reactants
Reaction pathway
Energy from Chemicols
()
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d
d
Which of the following energy changes indicates theactivation energy for the catalysed reaction?
AI B IIcilr Drv ( )
6. What effect does an increase in temperature have on theactivation energy and enthalpy change of a chemical reaction?
Activation energy Enthalpy change
A Unchanged U nchanged
B Decreases I ncreases
C Unchanged Decreases
D I ncreases Unchanged
1. Which of the following occurs in a hydrogen fuel cell?
A Hydrogen and oxygen react at the electrodes to formwater, generating electricrty.
B Water is split up at the electrodes to form hydrogen and
oxygen, generating electricity directly.C Hydrogen and oxygen react at the electrodes to form
water, generating heat energy which is then convertedto electricity.
D Water is split up at the electrodes to form hydrogen and
oxygen, releasing heat energy which is then convertedinto electricity (
)
B. Which of the following are ways of obtaining hydrogen foruse as fuel?
Electrolysis of waterCracking of petroleumFractional distillation of airBeaction of metals with dilute acids
Unit13 I tn*rgylrr:nCherricals 97
10. Which of the following is/are true for the reaction?
I The 0-H bond is weaker than the H-H or the 0 = 0 covalentbond.
ll Energy released in breaking the H-H and 0 = 0 bonds is
greater than the energy absorbed in forming the 0-H bonds.
lll Energy released in forming the 0-H bonds is greater thanthe energy absorbed in breaking the H-H and 0 = 0 bonds.
A ll only B lll onlyC I and ll only D I and lll only (
)
11. Which of the following is an exothermic reaction?
A Formation ofglucose and oxygen from carbon dioxide and
waterB Decomposition of calcium carbonate
C Heating of hydrated copper(ll) sulfate to form itsanhydrous form
D Beaction of aqueous sodium hydroxide and dilutehydrochloric acid ( )
12. Which of the following is an endothermic reaction?
A C{s)+ 0,(g) - C0lg)B H-(aq)+ 0H-(aq) - H,0(l)
C Ba2laq) + SOrF(aQ) - BaS0a(s)
D CH,C00H(aq)= CH,C00-(aq)+ H.(aq) (
13. Syngas is the name given t0 a gaseous fuel mixture containing
varying amounts of carbon monoxide and hydrogen. lt can be
made using the following reaction:
C(s)+ H,O(g) - C0(g)+ H,(g)
When steam is passed over white-hot coke, the coke willgradually cease t0 be white-hot and steam will begin tocondense on the coke. Before this happens, the steam is cutoff and hot air is sent in for a short interval. This cycle is thenrepeated.
Which of the f0llowing best explains the need for the hot air?
A To stop the exothermic reaction so as to prevent explosionB To burn up unnecessary impurities so as to avoid
contaminationC To constantly supply the endothermic reaction with
sufficient heat energyD To increase the temperature of the reactants so as t0
speed up the reaction ( )
14. When ice melts, the energy change of the process can beexpressed as follows:
H,O(s) + ll,g111 lH = +6.00 kJ/mol
Which of the following is true based on the above reaction?
A 6.00 kJ of heat is released when one mole of ice melts.B 6.00 kJ of heat is released when one mole of water
freezes.
C 6.00 kJ of heat is absorbed when one mole of steamcondenses.
D 6.00 kJ of heat is absorbed when one mole of liquid waterboils. ( )
\\,s
\\,g
M0
\\,g
\\,s
I
il
ilt
IV
AC
I and ll onlyll and lll only
B I and lV onlyD lll and lV only (
Refer to the following to answer questions 9 and 10.
Heat is given off when hydrogen burns in air according to the followingequation:
2H,(g) + 0,(g) - 2H,0(g) AH = -483.6 kJ
d9. Which of the following factors account for the enthalpychange observed in the above reactlon?
I The formation of 0-H bondsll The breaking of the 0-H bondslll The breaking of the H-H and 0 = 0 bondslV The formation of the H-H and 0 = 0 bonds
A I and lll only B I and lV onlyC ll and lll only D ll and lV onty (
)
()
)
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98 lheme 3 I Chemistry of Reoctions
15 Hydrogen combines through an endothermic reaction withiodine to form hydrogen iodide gas.
H,(g)+ l,(g) t 2Hl(g) AH = +26.5 kJ/mol
Which of the following is not true about the reaction?
A The energy content of the product is higher than that ofthe reactants.
B The activation energy needed for the reaction will be
greater than 26.5 kJ.
C The energy absorbed in bond-breaking is greater thanthat liberated in bond-forming.
D The combined bond energies oftwo H-l bonds are greater
than that of one H-H and one l-l bonds. ( )
U 16. Hydrogen reacts with chlorine to form hydrogen chloride gas
according to this equation:
H,(g)+ C/,(g) - ZHCtls) AH = -92.3 kJ/mol
Which of the following explains the heat change for thisreaction?
A The H-H and C/-Cl bonds are stronger than the H-C/bonds.
B [Volecules liberate energy when they combine to formnew compounds.
C The number of bonds formed is greater than the number
of bonds broken.
D The energy absorbed to break bonds is less than thatliberated to form bonds. (
)
\\,g 17. Ammonia reacts with oxygen to form nitrogen oxide and wateras follows:
+NH,(O) + 50,(u) - 4N0(s) + 6H,0(O) AH = -382 kJ/mol
Which of the following is not true?
A 382 kJ of heat will be evolved for each mole of NH,
reacted.
B The reverse reaction is endothermic with an enthalpychange of +382 kJ/mol.
C N0 and HrO have a total energy content greater than that
of NH, and 0, combined.
D The four N-0 and twelve 0-H bonds are stronger thanthe twelve N-H bonds and five 0 = 0 bonds. ( )
\V0 1 8. The energy profile diagram for a given catalysed reaction is
shown below:
Energy
Which of the following shows the correct energy profile
diagram for the uncatalysed reaction?
I Energy
products
reactants
Reactionpathway
B En".gy
reactants productsReactionpathway
f, Energy
reactants
I Energy
reactants
productsReactionpathway
Reactionpathway
reactants
Reaction pathway
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Refer to the following t0 answer questions 19 and 20.
The equation for the nickel-catalysed reaction of ethane and hydrogenis shown as follows:
NtiC,Ho(g)+ H,(g)-r5 C,Uo1g1 lH = -130 kJ/mol
The energy profile diagram for this reaction is shown below:
Energy
reactants
products
Extent of reaction
U 19. When could a reaction occur between a C,Ho molecule and
a H, molecule?
A Each time they collideB Only when they collide with energy exactly equal to YC 0nly when they collide with energy equal to or greater
than XD 0nly when they collide with energy equal to 0r greater
thanY ( )
\V0 20. Which of the following would be affected by the addition of
nickel to the above reaction?
A Xonly B YonlyC XandYonly D X,YandZ (
)
\Vg 21. Which of the following energy profile diagrams shows the
slowest endothermic reaction?
ABEnergy Energy
Reaction Reactionpathwaypathrvay
Energy Energy
Unil 13 I t.;;': ;:1.:: :.;;.1'.,'' | :.;'t-i ) i.'.. ;t:::': :,:'' /':' 99
22. Coal, petroleum and natural gas are known as fossil fuels. Thecombustion of an effective fossil fuel must have an activationenergy that is neither too high nor too low.
What happens if their combustions have very low activationenerg ies?
A They will ignite very easily and be hazardous.B They will evaporate too easily, causing high wastage.C They will produce too much greenhouse gases when
burnt.D They will not produce useful amounts of energy when
burnt. ( )
23. The following energy profile diagrams show the energychanges for the heating of one mole of four differentcompounds in air. Which energy profile diagram is for thecompound that shows the greatest potential for use as a fuel?
A Energy
reactants
products Reactionpathway
B Energy
reactantsproducts
Reactionpathrvay
(, Energy
products
reactantsReactionpathway
! Energy
Reactionpathway
1Y
Zi
x
\Vs
t\,0
C D
Reactionpathway
Reactionpathway
()
reactants
products
()
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1OO Theme 3 I Chemistrv of Reoctions
U 24. When the wick of a candle is touched by a lit match, thecandle begins to burn. When the match is removed, thecandle continues to burn. What is the role of the match in
the reaction involving the candle wax?
A lt acts as a catalyst.B lt supplies the activation energy.
C lt lowers the activation energy barrier.D lt increases the rate of the combustion. ( )
Refer to the following to answer questions 25 and26.
Hydrogen is increasingly being investigated as a fuel for the future.It burns in oxygen according to the following reaction:
2H,(g) + 0,(g) - 2H,0(l) AH = -571.8 kJ
\\,0 25. How much energy is released when 4.2 kg of hydrogen is
burnt in air?
A 3x105kJ B 6x105kJC 9x106kJ D 1.2x106kJ ( )
W,26. Which 0f the following describe(s)the advantages of carrying
out this reaction in a fuel cell rather than burning hydrogen
and converting the heat into electricity?
I lt reduces pollution to the environment.
ll Less energy is wasted or lost during conversion.
lll lt increases the ease of storage and handling of hydrogen.
A I only B ll only
C I and lll only D ll and lll only ( )
Refer to the following to answer questions 27 to30.
The following table compares the properties of four different fuels.
\Vg 27. Which of the following shows the correct order of fuelswhich produce decreasing amounts of energy when 1 g ofthe compound is completely burnt?
A Hydrogen, methane, petrol, ethanolB Hydrogen, methane, ethanol, petrol
C lVethane, hydrogen, petrol, ethanolD lVethane, hydrogen, ethanol, petrol ( )
28. Which of the following shows the conect order of fuels whichproduce decreasing amounts of energy when 1 litre of thecompound is completely burnt?
A Petrol, ethanol, hydrogen, methaneB Petrol, ethanol, methane, hydrogen
C Ethanol, petrol, hydrogen, methane
D Ethanol, petrol, methane, hydrogen ( )
29. Which 0f the following shows the correct order of fuelswhichproduce decreasing amounts of carbon dioxide per mole offuel used?
A Petrol, methane, ethanol, hydrogen
B Petrol, ethanol, methane, hydrogen
C [Vethane, ethanol, petrol, hydrogen
D Ethanol, petrol, methane, hydrogen ( )
30. lVethane in the form of compressed natural gas (CNG) is beingused as a fuel for cars.
Which of the following showthe advantages of using methaneas a car fuel compared to petrol?
I Produces more heat per unit of massll Enables cars to travel longer distances for each tank of
fuellll Produces lower levels of carbon dioxide per unit of energy
released
Mg
\Vg
w
U
A I and ll only
C lland lllonlyB I and lll onlyD l, ll and lll
31. Ethyne (CrHr) undergoes hydrogenatlon to form ethane as
follows:
C,H,(g)+ 2H,(g) - C,Hu(g)
The average energies of the bonds in the substances involved
are shown in the table below
Bond Bond energy/kJ mol-t
C_H 413
L-L 341
C=C 612
C=C 839
H-H 432
What is the enthalpy change for this reaction?
A -176 kJ/mol B -296 kJ/molC +176 kJ/mol D +296 kUmol
Property Ethanol Hydrogen Methane Petrol
lVolar mass/g 4b 2 tb 114
Density/kg l-1 0.79 6.4 x 10r 0.69
Entha I py
change of
combustion/
kJ molr
-1 360 -285 -891 -5460
()
B.4x 10 5
()
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Refer to the f0llowing t0 answer questions 32 and 33.
Hydrogen gas can be stored in metal hydride compounds undermoderate temperature and pressure, which gives them a safetyadvantage.
ln order to store hydrogen, the gas is passed sl ightly over atmosphericpressure over the metal alloy. Most metal alloys bind with hydrogenvery strongly to form the metal hydride. This reaction as shown belowis reversible and the gas can be released again.
lVetal(s) + Hydrogen(g) + [Vletal hydride(s)
W,, Which of the following energy prof ile diagrams bestrepresents the energy changes for the processes?
A Energy
metal hydride
metal + hydrogen
Reactionpathway
B Energy
metal
metal + hydrogen
Reactionpathway
Unit 13 I {"nergy fram Chery:iccls 101
33. Which of the following is required to release the hydrogenfrom the metal hydride for use in suitable applications?
A Cooling down the metal hydrideB Supplying heat energy t0 the metal hydrideC Beducing the pressure over the metal hydrideD lncreasing the pressure over the metal hydride ( )
34. Heat is given off when hydrogen burns in air according to theequation:
Equation l: 2Hlg)+ 0,(g) - 2H,0(g) AH = -483.6 kJ
The heat of reaction for the combustion of hydrogen in aircan also be expressed as follows:
Equation ll: 2H,(g)+ 0,(g) - 2H,0(l) AH = -571.8 kJ
ln this case, liquid water is formed instead of steam.
Which of the following explains why the value for AH inequation ll is different from that in equation l?
A Some heat energy is absorbed due to the condensationof steam to liquid water.
B Some heat energy is absorbed for the breaking of bonds
to form more liquid waterC lVore heat energy is released due to the condensation of
steam to liquid water.D lVore heat energy is released due to the formation of
more bonds to form more water. ( )
35. Which of the following statements is not true?
A Photosynthesis is an exothermic reaction.
B An exothermic reaction only needs heat to initiate.C An endothermic reaction requires a constant supply of
heat as long as the reaction proceeds.
D Beactions with high activation energies do not occurspontaneously and may require heat or the addition ofcatalyst to initiate the reaction. ( )
36. Which of the following only involves an exothermic process?
A C(s)+ 0,(s) - C0lg)g H,(s)+ C[(u) - 2HCl(s)
C Pb'?t(aq) +ZCl (aql - PbC/z(s)
D C/,(ao)+ 2Br(aq) - ZCt(aql + Br,(aQ) ( )
C Er".gy
U
W
w
W,metal + hydrogen
D Energy
metal hvdride
Reactionpathway
Reactionpathway
+ hydrogen
metal hydride
()
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1O2 Theme 3 I Chcrnistry r:f l?ecclions
37. The energy changes in the following reversible reaction is
shown in the energy profile diagram below.
2N,(g) + Hls) = zNH, (s)
Energy
w
w
What does X represent?
A Heat of reaction for the reverse reactionB Heat of reaction for the forward reaction
C The energy absorbed for the decomposition of NH,molecules
D The minimum energy needed to initiate the reaction ofthe N, and H, molecules (
)
x
Reaction progress
\[4838. The enthalpy changes for the reaction of hydrogen with the different halogens are shown below.
What deduction can be made based on the information in the table?
A Formation of H-l bond releases the greatest am0unt of energy.
B Compared to the other halogens, iodine forms the weakest bond with hydrogen
C Bond-breaking in the reaction of H, and
D Bond-breaking in the reaction of H, and
to form Hl requires the largest amount of energy.
to form HF requires the largest amount of energy
l2
F2
Nl4D39. Hydrochlorrc acid reacts with sodium hydroxide in an
exothermic reaction as shown:
HC/(aq)+ Na0H(aq) - NaC/(aq)+ H,0(l) AH, = -57 2 L..1
When ethanoic acid is used instead of hydrochloric acid, thereaction goes t0 completion as follows:
CH,CO0H(aq)+ Na0H(aq) - NaCHgCO0(aq)+ H,0(l)AH,=-554L''1
Why is the value of AH, different from that of AH,?
A Less heat energy is released due to less water formed.
B lVore heat energy is released due to more water formed.
C Some heat energy is absorbed for the dissociation ofethanoic acid molecules to form hydrogen ions.
D lVore heat energy is released due to the dissociation ofethanoic acid molecules to form hydrogen ions. ( )
40. Hydrogen undergoes combustion with oxygen according tothe following reaction:
H-H ,t0H-H +U=o ----------> Ht \H
0
H
AH = -488 kJ
The amount of energy needed to break the bonds in thereaction are shown below:
Bond Energy needed to break the bond/kJ
H-H 436
0=0 496
0-H X
What is the value of x?
H
A
C
?20
464
Halogen (X) Energy ol the X-X bond /kJ molr Beaction with hydrogen AH/kJ mol{
Fl uori ne F-F 158 Hr+ Fr+ fgp -273.3
Chlorine ct-ct242 Hr+ Clr- ZHCI -92.3
Bromine Br-Br 193 Hr+Brr- 2HBr -35.3
lodine l-l 1 51 Hr+lr+lX1 +25.4
B 222
D 710
()
()
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Wo Aqueous hydrochloric acid was added from a burette to25.0 cm3 of 1.50 mol/dm3 aqueous sodium hydroxide. The
temperature change was measured each time a portion ofthe acid was added.
The results of the experiment were plotted on a graph as
follows:
Temperature ('C)
Refer to the following t0 answer questions 42 and 43.
The table below gives information about some alkanes and alcohols.
U 42. What is the quantity of heat evolved from the combustionof 60 dm3 of propane, measured at room temperature and
pressure?
A s550 kJ B 5946 kJ
C 6660 kJ D 1.33 x 105 kJ ( )
Unit I3 I '.., .,,-),'i t'.;t. i-'-.; '::': :',t-..'-: 103
Based on the graph, which of the following statements is
true?
A Neutralisatron is complete at R.
B The sample of alkali has fully reacted at 0.C The reaction is exothermic from P to O, and becomes
endothermic when more acid is added.D The temperature increases from P to O because more heat
is absorbed in breaking of bonds than in the formation ofnew bonds. ( )
43. Which of the following deductions can be drawn from thedata given in the table?
I Each additional -CHr- group causes an increase ofapproximately 655 kJ of energy t0 the enthalpy change
of combustion of the alkanes.
ll The increase in enthalpy change of combustion due to
each additional *CH,- group for the alcohols is greater
than that observed for the alkanes.
lll Alcohols release less energy than the correspondingalkanes containing the same number of carbon atoms.
A I and ll only B I and lll only
C ll and lll only D l, ll and lll ( )
P
0
R
Total volume of acid added (cm3)
\V0
EXTENSION QUESTIONS
No. of carbon atoms Name of alkaneEnthalpy change of
combustion/kJ mol{ Name ol alcoholEnthalpy change of
combustion/kJ moli
1 It/etha ne -890 lt/ethanol -126
2 Ethane -1 560 Ethanol -1361
3 Propa ne -2220 Propanol -2021
4 Buta ne -2811 Butano I -2676
5 Pentane -3509 Pentanol -s329
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1O4 Theme 3 I Chenristry *f Reoctions
Refer to the following to answer questions 44 and 45.
Ethanoic acid reacts with sodium bicarbonate in an endothermicreaction.
Two experiments were conducted with a fixed volume of excess
aqueous ethanoic acid used in each case. The amount of sodium
carbonate used for the two experiments are as follows:
Experiment I 1 0.0 g of sodium bicarbonateExperiment ll 20.0 g of sodium bicarbonate
w44. Which of the following shows the graphs obtained for thetwo experiments?
A remperature
roomtemperature
Time
Temperature
temperature
Time
C Temperature
roomtemperature
I, II
Time
D Temperature
room
II
room
IItemperature
Time
U 45. ln the two experiments, which point on the graph shows thetime when the reaction first reaches completion?
Temperatul
Aroom
temperature
Time
The energy change for the reaction of magnesium withhydrochloric acid is shown by the following equation:
lVg(s) + 2HC/(aq) - I\4gC/,(aq) + HJg) AH = -460 kJ
Which of the following would result in the smallest rise intemperature?
A 24 g of magnesium added to 1.0 dm3 of 2.0 mol/dm3hydrochloric acid
B 48 g of magnesium added to 1.0 dm3 of 2.0 mol/dm3hydrochloric acid
C 48 g of magnesium added to 1.0 dm3 of 4.0 mol/dm3hydrochloric acid
D 144 g of magnesium added to 1.0 dm3 of 1.0 mol/dm3hydrochloric acid ( )
Befer to the following t0 answer questions 47 and 48.
The hydrated salt, sodium sulfate decahydrate (NarS0o .10H,0), wasamong the first to be studied as a material for the storage of solarenergy.
When sodium sulfate decahydrate is heated to 32'C and above,it releases its water of crystallisation and dissolves in it to forma solution. When the solution is cooled, the solid hydrated salt is
obtained again. This reversible reaction is as Jollows.
Na,SOo.1 0H,0(s) = Na,SOo(aq) + 1 0H,0(l)
NI4D47 What is true of this reversible reaction?
A The fonvard reaction releases more heatthan the reverse
reaction.
B The fonruard reaction absorbs less heat than the reverse
reaction.
C The forward reaction is endothermic and the reverse
reaction is exothermic.
D The forward reaction is exothermic and the reversereaction is endothermic { )
B
C
D
W*
B
I
)(
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NI4D48. The hydrated salt, when heated by solar energy, can thus be
used to store the energy for subsequent use.
Which of the following describe the storage of solar energyin the hydrated salt?
I There is a reversible change of state from solid to liquid.ll Temperature of the mixture rises as more and more solar
energy is absorbed.lll The solar energy absorbed is stored in the aqueous
solution and released to the surroundings when it cools.lV Temperature of the mixture remains the same as more and
more solar energy is absorbed until the fonvard reactionis complete.
A I and lV B ll and lllC l, lland lll D l,llland lV (
)
Unit l3 I tnerSy lrorrr Cherniccls 105
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