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Name:___________________________

Grade 11B/G Take Home Test #4

Thermochemistry Due Tuesday January 17th, 2017

___________________________________________________________________________________ Instructions:

Please answer each of the following questions in the space provided.

Test will be marked out of 100; each question is worth 5 marks

5 marks will be deducted per day late.

There will be no bonus questions.

Talk about heat transfer!

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1. How much heat is absorbed by 70.0g of water when the temperature of the water increases from 22.4°C to 86.6°C?

2. How much heat is required to raise the temperature of 20.0g of iron from 26.0°C to 72.3°C?

3. What is the specific heat of a metal if the temperature of a 28.4g sample of metal is increased by 8.1°C when 207J of

heat is added? What is the identity of the unknown metal?

4. What is the specific heat of silicon if the temperature of a 4.11g sample of silicon is increased by 3.8°C when 11.1J of

heat is added?

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5. When a 1.74g sample of an unknown metal at 70.000°C is placed in a calorimeter containing 50.0g of water, the

temperature changes from 24.000°C to 24.194°C. What is the specific heat of the metal? What is the identity of the

metal?

6. What is the specific heat of an unknown metal if the temperature of a 8.21g sample is increased by 6.2°C when 6.51J of

heat is added? What is the identity of the unknown metal?

7. Which of the statements about the following enthalpy diagram is FALSE?

A)

The H of this reaction is -250 kJ.

B)

The product of this reaction is stable.

C)

The H of this reaction is +250 kJ

D)

The enthalpy of the products is -250 kJ

enthalpy (kJ)

reaction progress

250

200

150

100

50

0

- 50

- 100

- 150

- 200

- 250

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8. Which statement correctly describes an endothermic chemical reaction?

a. The products have higher potential energy than the reactants, and the ∆H is negative. b. The products have higher potential energy than the reactants, and the ∆H is positive. c. The products have lower potential energy than the reactants, and the ∆H is negative. d. The products have lower potential energy than the reactants, and the ∆H is positive.

9. A substance increases in temperature by 255ºC when a 983 g sample of it absorbs 83 200 J of heat. What is the specific heat capacity of the substance?

a) 321 J/g˚C b) 0.332 J/g˚C c) 0.450 J/g˚C d) 21.6 J/g˚C 10. The ∆H for the solution process when solid sodium hydroxide dissolves in water is -44.4 kJ/mol. When a 13.9 g sample of NaOH dissolves in 250.0 g of water in a coffee-cup calorimeter, the temperature increases from 23.0˚C to ________˚C. Assume that the solution has the same specific heat as liquid water, i.e., 4.18 J/g ˚C.

a) 35.2˚C b)14.0˚C c) 37.8˚C d) 40.2˚C e) 37.0˚C 11. Equal masses of two substances, A and B, each absorb 25 Joules of energy. If the temperature of A increases by 4 degrees and the temperature of B increases by 8 degrees, one can say that:

a) the relationship between the specific heat capacities cannot be determined b) the specific heat capacities of A and B are 4 units apart. c) the specific heat capacity of A is double that of B d) the specific heat capacity of B is double that of A

Please explain your reasoning:

12. Indicate whether the sentence or statement is true or false.

a In calorimetry, the assumption is made that the enthalpy change of the system equals the heat transferred to the surroundings._____

b. The burning of gasoline is an example of an endothermic physical change._____

c. An endothermic reaction will decrease the temperature of its surroundings._____

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13. Given the graph below for the reaction: A+B C + D: (4 points each) a. The heat content of the reactants of the forward reaction is ________kilojoules. b. The heat content of the activated complex of the reverse reaction is ________kilojoules. c. The activation energy of the forward reaction is about ________kilojoules. d. The heat of reaction (ΔH) of the reverse reaction is ________kilojoules. e. The heat content of the reactants of the reverse reaction is ________kilojoules. f. The heat content of the activated complex of the forward reaction is ________kilojoules. g. The activation energy of the reverse reaction is ________kilojoules. h. Please write a complete equation for this reaction, showing the enthalpy.

d. Specific heat capacity is the amount of heat required to change a given mass through 1°C._____

e. When mixing two substances of equal temperature, the final temperature will always be the same. _____

f. In exothermic reactions, the reactants have more kinetic energy than the products._____

h. On a potential energy diagram, the horizontal axis may be called reaction progress._____

i. In endothermic reactions, the heat term is written on the right side of the equation._____

j. If the specific heat capacities of two substances at different temperatures are the same, mixing them will yield a temperature that is the average of the two initial temperatures.____

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14. When a certain substance with a mass of 100 grams is heated from 25˚C to 75˚C, it absorbed 4500 Joules of heat energy. Calculate the specific heat of the substance, and identify it using the following table: (10 points)

Water: 4.184 J/g ˚C Ice: 2.1 J/g ˚C Aluminum: 0.90 J/g ˚C Silver: 0.24 J/g ˚C Mercury: 0.14 J/g ˚C

15. Consider the following reaction:

2 Mg(s) + O2(g) → 2MgO(s) H = 1204kJ a) Is this reaction exothermic or endothermic? Explain your choice. (4 points) b) Draw a complete (labeled) enthalpy diagram for this reaction. (6 points)

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16. A 0.2808g sample of glucose, C6H12O6, is burned in a bomb calorimeter. The temperature is noted to rise from 25.11˚C to 27.21 ˚C. If the molar heat of combustion is 2803 KJ: a) Write the balanced thermochemical equation (i.e. the reaction showing ∆H) b) Determine the specific heat capacity of the calorimeter?

17. A 0.500 g sample of TNT (C7H5N2O6) is burned in a bomb calorimeter containing 610 grams of water at an initial temperature of 20.00˚C. The heat capacity of the calorimeter is 650 J/g˚C and the heat of combustion of TNT is 3374 kJ/mol. Using these data, calculate the final temperature of the water and calorimeter once the reaction is complete.

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18. Which diagram represents the following reaction?

O 2/3 + Al 2 2(g)(s) kJ421 1 + OAl 3(s)2

19. .If you were to order a cup of coffee, would you want the cup to have a high heat capacity or a low heat capacity before you carry it out? Please explain your answer.

Enthalpy

-1 421

0

Progression of the reaction

B)

2Al O 3(s)2 Al 2(g)(s) + 3/2 O

2 Al (s) + 3/2 O 2(g)Al 2 O 3(s)

Enthalpy

-1 421

0

Progression of the reaction

A)Enthalpy

1 421

0

Progression of the reaction

C)

2 Al (s) + 3/2 O 2(g)

Al 2 O 3(s)

Enthalpy

1 421

0

D)

2 Al (s) + 3/2 O 2(g)

Al 2 O 3(s)

Progression of the reaction

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20. The graph below illustrates a variation in enthalpy (H) :

ENTHALPY (kJ)

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NH + Cl

Time

4 (s)

4 (aq) (aq)+ -

NH Cl

0

Which of the following equations best represents the graph?

A)

NH4

+(aq) + Cl-(aq) NH4Cl(s) + 16.2 kJ

B)

NH4Cl(s) NH4

+(aq) + Cl-(aq) + 16.2 kJ

C)

NH4Cl(s) + 16.2 kJ NH4

+(aq) + Cl-(aq)

D)

NH4

+(aq) + Cl-(aq) + 16.2 kJ NH4Cl(s)

21. Following the neutralization of a solution of dilute potassium hydroxide (KOH(aq)) with a solution of 0.50 mol/L hydrochloric acid (HCl(aq)), you note the following results :

Before neutralization

After neutralization

KOH(aq)

HCl(aq) 0.50 mol/L

Mixture

Volume (mL)

T1(°C)

Volume (mL)

T1(°C)

Volume (mL)

T/(°C)

100

22.0

50

22.0

150

24.5

What is the value of the molar heat (H) of neutralization of hydrochloric acid?

A) -1.6 kJ/mol

B) -3.2 kJ/mol

C) -3.2 x 101 kJ/mol

D) -6.4 x 101 kJ/mol

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22. Identify the exothermic reactions from the following. (for this question only there may be more than one answer, for full marks you must select all the correct ones!).

OH 1. (g)2 Energy + OH (l)2

O 2/1 + H 2. 22 kJ 241.8- = OH2 H

Heat + SOH 3. 4(l)2 O2 + S 8/1 + H 2(g)8(s)2(g)

O + N 4. 2(g)2(g) kJ 180.8+ = NO 2 (g) H

O + C 5. 2(g)(s) kJ394 + CO2(g)

23. Compound A is burned in a bomb calorimeter that contains 2.50 liters of water. If the combustion of 0.175 moles of this compound causes the temperature of the water to rise 45.00 C, what is the molar heat of combustion of compound A? The heat capacity of water is 4.184 J / g0C.

24. Compound B is burned in a bomb calorimeter that contains 1.50 liters of water. When I burned 50.0 grams of compound B in the calorimeter, the temperature rise of the water in the calorimeter was 35.00 C. If the heat of combustion of compound B is 2,150 kJ/mol, what is the molar mass of compound B?

25. The molar heat of combustion of compound C is 1,250 kJ/mol. If I were to burn 0.115 moles of this compound in a bomb calorimeter with a reservoir that holds 2.50 L of water, what would the expected temperature increase be?

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26. A 75.5 kg student at a temperature of 36.6 oC jumps into a hot tub containing 160,000 mL of water on a cold winter’s day. The water, which is initially at a temperature of 39.856 oC, cools down to a temperature of 38.652 oC and oddly enough, the student warms up to that same temperature after a 35 minute soak. Calculate the specific heat of the student, assuming that no heat is lost in the exchange.

27. If I burn 0.315 moles of hexane (C6H14) in a bomb calorimeter containing 5.65 liters of water, what’s the molar heat of combustion of hexane is the water temperature rises 55.40 C? The heat capacity of water is 4.184 J/g0C. 28. Compound A is burned in a bomb calorimeter that contains 2.50 liters of water. If the combustion of 0.175 moles of this compound causes the temperature of the water to rise 45.0˚ C, what is the molar heat of combustion of compound A? The heat capacity of water is 4.184 J / g˚C.

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29. The molar heat of combustion of compound C is 1,250 kJ/mol. If I were to burn 0.115 moles of this compound in a bomb calorimeter with a reservoir that holds 2.50 L of water, what would the expected temperature increase be? 30. Magnesium burns in oxygen according to the following equation:

Mg(s) + 2

1 O2(g) MgO(s) H = 6.00 102

mol

kJ

If 6.00 g of magnesium metal is burned in an excess of oxygen, what energy will be released by this reaction?

A)

1.48 102 Kj

B)

1.92 102 kJ

C)

3.60 102 kJ

D)

2.43 103 kJ

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31. In order to determine how much heat is released during the combustion of candle wax, C25H52, a burning candle is used to heat some water in a metal can that serves as a calorimeter. The following data is obtained:

Volume of water heated

355.0 mL

Initial mass of candle

136.0 g

Final mass of candle

112.0 g

Initial temperature of the water

15.4°C

Final temperature of the water

23.0°C

Calculate the molar heat of combustion of the candle wax.

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