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COLEGIO CATÓLICO JOSÉ ENGLING
EDUCAR AL HOMBRE NUEVO PARA EL MUNDO DEL MAÑANA
ENERGÍA EN LAS REACCIONES QUÍMICAS (TERMOQUÍMICA)
CURSO: 2º de bachillerato
RESUELVA LOS SIGUIENTES PROBLEMAS:
Recuerde que para los problemas de opción múltiple no puede utilizar calculadora, solamente la tabla periódica del cuadernillo de datos. Para los problemas de desarrollo puede utilizar la calculadora y el cuadernillo de datos
1. When 100 cm3 of 1.0 mol dm–3 HCl is mixed with 100 cm3 of 1.0 mol dm–3 NaOH, the temperature of the resulting solution increases by 5.0 °C. What will be the temperature change, in °C, when 50 cm3 of these two solutions are mixed?
A. 2.5
B. 5.0
C. 10
D. 20(Total 1 mark)
2. Which statement about bonding is correct?
A. Bond breaking is endothermic and requires energy.
B. Bond breaking is endothermic and releases energy.
C. Bond making is exothermic and requires energy.
D. Bond making is endothermic and releases energy.(Total 1 mark)
3. Consider the following reactions.
Cu2O(s) + 21
O2(g) → 2CuO(s) ∆HO = –144 kJCu2O(s) → Cu(s) + CuO(s) ∆HO = +11 kJ
What is the value of ∆HO, in kJ, for this reaction?
Cu(s) + 21
O2(g) → CuO(s)
A. –144 + 11
B. +144 – 11
C. –144 – 11
D. +144 + 11(Total 1 mark)
4. Consider the two reactions involving iron and oxygen.
2Fe(s) + O2(g) → 2FeO(s) ∆HO = –544 kJ4Fe(s) + 3O2(g) → 2Fe2O3(s) ∆HO = –1648 kJ
What is the enthalpy change, in kJ, for the reaction below?
4FeO(s) + O2(g) → 2Fe2O3(s)
A. –1648 – 2(–544)
B. –544 – (–1648)
C. –1648 – 544
D. –1648 – 2(544)(Total 1 mark)
5. Which processes have a negative enthalpy change?
I. 2CH3OH(l) + 3O2(g) → 2CO2(g) + 4H2O(l)
II. HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
III. H2O(g) → H2O(l)
A. I and II only
B. I and III only
C. II and III only
D. I, II and III
6. Consider the following reactions.
N2(g) + O2(g) → 2NO(g) ∆HO = +180 kJ2NO2(g) → 2NO(g) + O2(g) ∆HO = +112 kJ
What is the ∆HO value, in kJ, for the following reaction?
N2(g) + 2O2(g) → 2NO2(g)
A. –1 × (+180) + –1 × (+112)
B. –1 × (+180) + 1 × (+112)
C. 1 × (+180) + –1 × (+112)
D. 1 × (+180) + 1 × (+112)(Total 1 mark)
7. Propane can be formed by the hydrogenation of propene.
CH3CH=CH2(g) + H2(g) → CH3CH2CH3(g)
(i) State the conditions necessary for the hydrogenation reaction to occur.
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(ii) Enthalpy changes can be determined using average bond enthalpies. Define the term average bond enthalpy.
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(iii) Determine a value for the hydrogenation of propene using information from Table 10 of the Data Booklet.
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(iv) Explain why the enthalpy of hydrogenation of propene is an exothermic process.
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(Total 7 marks)
8. Which equation represents the bond enthalpy for the H–Br bond in hydrogen bromide?
A. HBr(g) → H(g) + Br(g)
B. HBr(g) → H(g) + Br(l)
C. HBr(g) → H(g) + 21
Br2(1)
D. HBr(g) → H(g) + 21
Br2(g)(Total 1 mark)
9. Which types of reaction are always exothermic?
I. Neutralization
II. Decomposition
III. Combustion
A. I and II only
B. I and III only
C. II and III only
D. I, II and III(Total 1 mark)
10. A pure aluminium block with a mass of 10 g is heated so that its temperature increases from 20 °C to 50 °C . The specific heat capacity of aluminium is 8.99 × 10–1 J g–1 K–1. Which expression gives the heat energy change in kJ?
A. 10 × 8.99 × 10–1 × 303
B. 10 × 8.99 × 10–1 × 30
C. 10003031099.810 1
D. 1000301099.810 1
(Total 1 mark)
11. In an experiment to measure the enthalpy change of combustion of ethanol, a student heated a copper calorimeter containing 100 cm3 of water with a spirit lamp and collected the following data.
Initial temperature of water: 20.0 °CFinal temperature of water: 55.0 °CMass of ethanol burned: 1.78 gDensity of water: 1.00 g cm–3
(i) Use the data to calculate the heat evolved when the ethanol was combusted.(2)
(ii) Calculate the enthalpy change of combustion per mole of ethanol.(2)
(iii) Suggest two reasons why the result is not the same as the value in the Data Booklet.(2)
(Total 6 marks)
12. The standard enthalpy changes for the combustion of carbon and carbon monoxide are shown below.
C(s) + O2(g) → CO2(g) ∆HcO = –394 kJmol–1
CO(g) + 21
O2(g) → CO2(g) ΔHcO = –283 kJ mol–1
What is the standard enthalpy change, in kJ, for the following reaction?
C(s) + 21
O2(g) → CO(g)
A. –677
B. –111
C. +111
D. +677(Total 1 mark)
13. Which is correct about energy changes during bond breaking and bond formation?
Bond breaking Bond formation
A. exothermic and ∆H positive endothermic and ∆H negative
B. exothermic and ∆H negative endothermic and ∆H positive
C. endothermic and ∆H positive exothermic and ∆H negative
D. endothermic and ∆H negative exothermic and ∆H positive(Total 1 mark)
Which processes are exothermic?
I. Ice melting
II. Neutralization
III. Combustion
A. I and II only
B. I and III only
C. II and III only
D. I, II and III(Total 1 mark)
14. Which statement is correct given the enthalpy level diagram below?
A. The reaction is endothermic and the products are more thermodynamically stable than the reactants.
B. The reaction is exothermic and the products are more thermodynamically stable than the reactants.
C. The reaction is endothermic and the reactants are more thermodynamically stable than the products.
D. The reaction is exothermic and the reactants are more thermodynamically stable than the products.
(Total 1 mark)
15. Identical pieces of magnesium are added to two beakers, A and B, containing hydrochloric acid.Both acids have the same initial temperature but their volumes and concentrations differ.
Which statement is correct?
A. The maximum temperature in A will be higher than in B.
B. The maximum temperature in A and B will be equal.
C. It is not possible to predict whether A or B will have the higher maximum temperature.
D. The temperature in A and B will increase at the same rate.(Total 1 mark)
16. Which equation best represents the bond enthalpy of HCl?
A. HCl(g) → H+(g) + Cl–(g)
B. HCl(g) → H(g) + Cl(g)
C. HCl(g) → 21
H2(g) + 21
Cl2(g)
D. 2HCl(g) → H2(g) + Cl2(g)(Total 1 mark)
17. The data below are from an experiment to measure the enthalpy change for the reaction of aqueous copper(II) sulfate, CuSO4(aq) and zinc, Zn(s).
Cu2+(aq) + Zn(s) → Cu(s) + Zn2+(aq)
50.0 cm3 of 1.00 mol dm–3 copper(II) sulfate solution was placed in a polystyrene cup and zinc powder was added after 100 seconds. The temperature-time data was taken from a data-logging software program. The table shows the initial 23 readings.
A straight line has been drawn through some of the data points. The equation for this line is given by the data logging software as
T = –0.050t + 78.0
where T is the Temperature at time t.
(a) The heat produced by the reaction can be calculated from the temperature change, ΔT, using the expression below.
Heat change = Volume of CuSO4(aq) × Specific heat capacity of H2O × ∆T
Describe two assumptions made in using this expression to calculate heat changes.
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(b) (i) Use the data presented by the data logging software to deduce the temperature change, ∆T, which would have occurred if the reaction had taken place instantaneously with no heat loss.
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(ii) State the assumption made in part (b)(i).
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(iii) Calculate the heat, in kJ, produced during the reaction using the expression given in part (a).
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(c) The colour of the solution changed from blue to colourless. Deduce the amount, in moles, of zinc which reacted in the polystyrene cup.
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(d) Calculate the enthalpy change, in kJ mol–1, for this reaction.
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(Total 8 marks)
18. An experiment was designed to investigate how the enthalpy change for a displacement reaction relates to the reactivities of the metals involved. The following metals in order of decreasing reactivity were available.
Excess amounts of each metal were added to 1.00 mol dm–3 copper(II) sulfate solution.The temperature change was measured and the enthalpy change calculated.
(i) Suggest a possible hypothesis for the relationship between the enthalpy change of the reaction and the reactivity of the metal.
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(ii) Sketch a graph on the diagram below to illustrate your hypothesis.
(1)(Total 2 marks)
19. Hydrazine is a valuable rocket fuel.
The equation for the reaction between hydrazine and oxygen is given below.
N2H4(g) + O2(g) → N2(g) + 2H2O(g)
Use the bond enthalpy values from Table 10 of the Data Booklet to determine the enthalpy change for this reaction.
(Total 3 marks)
20. When some solid barium hydroxide and solid ammonium thiosulfate were reacted together, the temperature of the surroundings was observed to decrease from 15 ºC to – 4 ºC. What can be deduced from this observation?
A. The reaction is exothermic and ∆H is negative.
B. The reaction is exothermic and ∆H is positive.
C. The reaction is endothermic and ∆H is negative.
D. The reaction is endothermic and ∆H is positive.(Total 1 mark)
21. Which process represents the C–Cl bond enthalpy in tetrachloromethane?
A. CCl4(g) → C(g) + 4Cl(g)
B. CCl4(g) → CCl3(g) + Cl(g)
C. CCl4(l) → C(g) + 4Cl(g)
D. CCl4(l) → C(s) + 2Cl2(g)(Total 1 mark)
22. Some water is heated using the heat produced by the combustion of magnesium metal. Which values are needed to calculate the enthalpy change of reaction?
I. The mass of magnesium
II. The mass of the water
III. The change in temperature of the water
A. I and II only
B. I and III only
C. II and III only
D. I, II and III(Total 1 mark)
23. 1.0 g of sodium hydroxide, NaOH, was added to 99.0 g of water. The temperature of the solution increased from 18.0 ºC to 20.5 ºC. The specific heat capacity of the solution is4.18 J g–1 K–1.Which expression gives the heat evolved in kJ mol–1?
A. 0.40100018.40.1005.2
B. 0.40100018.40.1005.2
C. 10000.4018.40.1005.2
D. 10000.4018.40.15.2
(Total 1 mark)
24. Two students were asked to use information from the Data Booklet to calculate a value for the enthalpy of hydrogenation of ethene to form ethane.
C2H4(g) + H2(g) → C2H6(g)
John used the average bond enthalpies from Table 10. Marit used the values of enthalpies of combustion from Table 12.
(a) Calculate the value for the enthalpy of hydrogenation of ethene obtained using the average bond enthalpies given in Table 10.
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(b) Determine the value for the enthalpy of hydrogenation of ethene using the values for the enthalpies of combustion of ethene, hydrogen and ethane given in Table 12.
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(c) Suggest one reason why John’s answer is slightly less accurate than Marit’s answer and calculate the percentage difference.
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(d) John then decided to determine the enthalpy of hydrogenation of cyclohexene to produce cyclohexane.
C6H10(l) + H2(g) → C6H12(l)
(i) Use the average bond enthalpies to deduce a value for the enthalpy of hydrogenation of cyclohexene.
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(ii) The percentage difference between these two methods (average bond enthalpies and enthalpies of combustion) is greater for cyclohexene than it was for ethene. John’s hypothesis was that it would be the same. Determine why the use of average bond enthalpies is less accurate for the cyclohexene equation shown above, than it was for ethene. Deduce what extra information is needed to provide a more accurate answer.
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(Total 9 marks)
25. What is the energy, in kJ, released when 1.00 mol of carbon monoxide is burned according to the following equation?
2CO(g) + O2(g) → 2CO2(g) ΔHo = –564 kJ
A. 141
B. 282
C. 564
D. 1128(Total 1 mark)
26. The specific heat of iron is 0.450 J g–1 K–1. What is the energy, in J, needed to increase the temperature of 50.0 g of iron by 20.0 K?
A. 9.00
B.22.5
C. 45.0
D. 450(Total 1 mark
27. Which of the following reactions are exothermic?
I. CH4 + 2O2 → CO2 + 2H2O
II. NaOH + HCl → NaCl + H2O
III. Br2 → 2Br
A. I and II only
B. I and III only
C. II and III only
D. I, II and III(Total 1 mark)
28. Consider the reaction between magnesium and hydrochloric acid. Which factors will affect the reaction rate?
I. The collision frequency of the reactant particles
II. The number of reactant particles with E ≥ Ea
III. The number of reactant particles that collide with the appropriate geometry
A. I and II only
B. I and III only
C. II and III only
D. I, II and III(Total 1 mark)
29. Which substance does not conduct electricity?
A. Solid zinc
B. Molten zinc
C. Solid zinc chloride
D. Molten zinc chloride(Total 1 mark)
30. Which is true for a chemical reaction in which the products have a higher enthalpy than the reactants?
Reaction ∆H
A. endothermic positive
B. endothermic negative
C. exothermic positive
D. exothermic negative(Total 1 mark)
31. In a reaction that occurs in 50 g of aqueous solution, the temperature of the reaction mixture increases by 20 °C. If 0.10 mol of the limiting reagent is consumed, what is the enthalpy change (in kJ mol–1) for the reaction? Assume the specific heat capacity of the solution= 4.2 kJ kg–1 K–1.
A. –0.10 × 50 × 4.2 × 20
B. –0.10 × 0.050 × 4.2 × 20
C. 10.0202.450
D. 10.0202.4050.0
(Total 1 mark)
32. Use the average bond enthalpies below to calculate the enthalpy change, in kJ, for the following reaction.
H2(g) + I2(g) → 2HI(g)
Bond Bond energy / kJ mol–1
H–H 440
I–I 150
H–I 300
A. +290
B. +10
C. –10
D. –290(Total 1 mark)
33. How much energy, in joules, is required to increase the temperature of 2.0 g of aluminium from 25 to 30 °C? (Specific heat of Al = 0.90 J g–1 K–1).
A. 0.36
B. 4.5
C. 9.0
D. 54(Total 1 mark)
34. Which combination is correct for a chemical reaction that absorbs heat from the surroundings?
Type of reaction ΔH at constant pressure
A. Exothermic Positive
B. Exothermic Negative
C. Endothermic Positive
D. Endothermic Negative(Total 1 mark)
35. Using the equations below:
C(s) + O2(g) → CO2(g) ∆Hο = –394 kJ mol–1
Mn(s) + O2(g) → MnO2(s) ∆Hο = –520 kJ mol–1
What is ∆H, in kJ, for the following reaction?
MnO2(s) + C(s) → Mn(s) + CO2(g)
A. 914
B. 126
C. –126
D. –914(Total 1 mark)
36. The data below is from an experiment used to measure the enthalpy change for the combustion of 1 mole of sucrose (common table sugar), C12H22O11(s). The time-temperature data was taken from a data-logging software programme.
Mass of sample of sucrose, m = 0.4385 g
Heat capacity of the system, Csystem = 10.114 kJ K–1
(a) Calculate ΔT, for the water, surrounding the chamber in the calorimeter.
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(b) Determine the amount, in moles, of sucrose.
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(c) (i) Calculate the enthalpy change for the combustion of 1 mole of sucrose.
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(ii) Using Table 12 of the Data Booklet, calculate the percentage experimental error based on the data used in this experiment.
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(d) A hypothesis is suggested that TNT, 2-methyl-1,3,5-trinitrobenzene, is a powerful explosive because it has:
• a large enthalpy of combustion• a high reaction rate• a large volume of gas generated upon combustion
Use your answer in part (c)(i) and the following data to evaluate this hypothesis:
Equation for combustion Relativerate of
combustion
Enthalpy ofcombustion/ kJ mol–1
Sucrose C12H22O11(s) + 12O2(g) 12CO2(g) + 11H2O(g) Low
TNT 2C7H5N3O6(s) 7CO(g) + 7C(s) + 5H2O(g) + 3N2(g) High 3406
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(Total 7 marks)