# Thermodynamics Unit - Mounds Park Academy

Μηχανική

27 Οκτ 2013 (πριν από 4 χρόνια και 8 μήνες)

113 εμφανίσεις

Thermodynamics Unit

Heat Transfers

Heat in Phase Changes

Thermochemical Equations

Heat Transfers: pp. 293

298

Heat in Phase Change: pp. 307
-

221

Thermochemical Equations
: pp. 303

306

Assignment 1:

Heat Problems

1.

How much heat does 32.0 g of water absorb when it is heated from 25.0
o
C to
80.0
o
C?

q =
32.0g x 4.18

j

x 55.0
o
C =
7360 j

g
o
C

2.

How much heat is absorbed when 88.0 g of wate
r is heated from 5
o
C to 37
o
C?

q =
88.0g x 4.18

j

x 32
o
C =
10,000 j

*this is
rounded to

g
o
C

one digit
because of

t
he 5
o
C

3.

When 435 J of heat is added to 3.4 g of olive oil at 21
o
C
, the
temperature
increases to
85.
o
C. What is the specific heat of olive oil?

435 j = 3.4g x C x 64
o
C =
2.00

j

g
o
C

Would olive oil or water have a larger temperature change given the same amount
of energy?

The olive

oil would have a greater temperature change because it has

a smaller specific heat. (Takes less energy to raise the temp 1
o
C)

4.

1500 joules of heat are added to 50.0g of water. How much would the
temperature change? Would the temperature increase or

decrease?

1500 j = 50.0g x 4.18

j

x

t =
7.2
o
C

g
o
C

5.

How many joules are required to heat 100.0g of copper from 10.0
o
C to 100.0
o
C?

q = 100.0g x 0.385

j

x 90.0
o
C =
347 j

g
o
C

The same quantity of heat is added to 100.0g of aluminum at 10.0
o
C. W
hich gets
hotter, the copper or the aluminum? Explain.

The Cu gets hotter because it have a lower specific heat than Al.

6.

A 15.0g sample of metal at 100.0
o
C is added to 100.0g of water at 21.0
o
C. The
temperature of the water increases to 22.2
o
C. What

is the specific heat of the
metal?

q H
2
O absorbed = 100.0g x 4.18

j

x 1.2
o
C = 502 j from metal

g
o
C

502 j released by metal = 15.0g metal x C of metal x 77.8
o
C

C = 0.430

j

g
o
C

7.

A 10.0g sample o
f copper that was 100.0
o
C was added to a sample of water at
25.0
o
C. The temperature of the water increased to 35.0
o
C. What was the mass of
the water sample?

q metal = 10.0g x 0.385

j

x 65.0
o
C = 250. joules

g
o
C

250. j abs
orbed from metal = m x 4.18

j

x 10.0
o
C

g
o
C

m = 5.98g H
2
O

8.

One gram of anthracite coal when burned evolves about 7300 calories. What
weight of coal is required to heat 4.0 liters of water from room temperature
(20.0
o
C) to
the boiling point (100.0
o
C)?

q to heat H
2
O = 4000g x 1.00

cal

x 80.0
o
C = 320000 cal

g
o
C

32000 cal needed, 1 gram generates 7300 cal, so

32000 cal

=
44g of anthracite

7300 cal

Assignment 2:

Heat in Phase Chan
ges

1.

What energy is required to change 1 gram of water at 100
o
C to steam at 100
o
C?

540 cal

are required (called the heat of vaporization)

2.

How much energy is required to change 100 moles of water at 0
o
C to ice at 0
o
C?

100 moles x

18.0
15
g

= 1801.5

g of water

1 mole

1801.5g x 80.0 cal/g = 144,120

cal =
100,000 to 1 sig fig

3.

How much heat does it take to vaporize 1.0 moles of water at 100
o
C?

1.0 mole H
2
O x

18.015g

= 18.07g H
2
O

1 mole H
2
O

18.015g H
2
O x 540 cal/g = 9728 cal =
9700cal to 2 sig fig

4.

How much heat is liberated when 18.0g of water vapor turns into rain?

1.0 mole H
2
O x

18.015g

= 18.07g H
2
O

1 mole H
2
O

18.015g H
2
O x 540 cal/g = 9728 cal

=
9700cal to 2 sig fig

5.

How much heat is removed from your hand when 18g of snow melts on your
glove?

18g x 80.0 cal/g = 1440 cal =
1400 cal to 1 sig fig

6.

How much heat is liberated when 450.0g of steam at 100
o
C is changed to water
at
20
o
C?

450.0g 540 cal/g = 243000cal

total = 280,000cal

450.0g x 1

cal

x 80.0
o
C = 36000cal

to 2 sig fig

g
o
C

7.

Calculate the amount of heat required to convert 20.0g of ice at 0.0
o
C to steam at
100
o
C.

20.0g x
80.0 cal/g = 1600 cal

total =
14400

cal

20.0g x

1

cal

x 100.0
o
C = 2000 cal
to 3 sig fig

g
o
C

20.0g x 540 cal/g = 10800cal

8.

Calculate the amount of heat required to convert 15.0g of ice at
-
8.0
o
C to

steam at
105.0
o
C. (Specific heats: ice = 0.500cal/g
o
C; water = 1.00cal/g
o
C; steam =
0.480cal/g
o
C)

15.0g x 0.500

cal

x 8.0
o
C = 60. cal

g
o
C

15.0g x 80.0 cal/g = 1200 cal

total = 11000 cal

15.0g x 1

cal

x 100.0
o
C = 1500 cal

to 2 sig fig

g
o
C

15.0g x 540 cal/g = 8100 cal

15.0g x 0.480

cal

x 5
.0
o
C = 36 cal

g
o
C

9.

Calculate the heat evolved when 65.0g of liquid at 0.0
o
C forms ice at 0.0
o
C.

65
.0g x 80.0 cal/g = 5200 cal or
5.20 x 10
3

cal to 2 sig fig

10.

Calculate the amount of heat required to liquefy 20.0g of alcohol at its freezing
point. (Heat of fusion for alcohol is 24.9cal/g)

20.0g x 24.9 cal/g =
498 cal

Assignment
3:

Thermochemical Equations Given Heat of
Reaction.

1.

Define

a. endothermic
a reaction in which energy is absorbed

b. exothermic
a reaction in which energy is released

c. enthalpy
heat (energy) changes in a reaction

2.

For the reaction:

C
8
H
18

(l) +

25/2 O
2

(g)

8 CO
2
(g) + 9 H
2
O (g) + 1300 kJ

a.

Is the reaction exothermic or endothermic?
exothermic

b.

How much energy is released when 456.0g of C
8
H
18

burns?

456,0g C
8
H
18

x

1 mole C
8
H
18

x

1300kJ

=
5190kJ

114.22g C
8
H
18

1 mole C
8
H
18

c.

H =
-

1300kJ

d.

How does the energy of the reactants compare to the energy of the products?
Draw a sketch of the graph of energy vs. time.

3.

For the reaction:

2 CO
2

(g)

2 CO (g) + O
2

(g)

H = +43.9 kJ

a.

Write the ther
mochemical equation (put the heat in the equation).

43.9kJ + 2 CO
2

(g)

㈠2O (朩† ⁏
2

(g)

b.

Is the reaction exothermic or endothermic?

endothermic

c.

How much energy is required to decompose 5.0L of CO
2

gas?

5.0L CO
2

x

1 mole CO
2

x

43.
9kJ

=
46kJ

22.4L CO
2

2 mole CO
2

d.

How does the energy of the products compare to the energy of the reactants?

The energy of the products is higher than the energy of the reactants.

e.

How much energy is needed to form 64.0g of O
2

gas?

64g O
2

x

1 mole O
2

x

43.9kJ

=
88kJ

32.00g O
2

1 mole O
2

f.

How many grams of CO
2

gas can be decomposed when 29 kJ of energy is
available?

29kJ x

2 mole CO
2

x

44.04g CO
2

=
58g CO
2

43.9kJ

1
mole CO
2

g.

What is the energy released per mole of carbon monoxide?

1 mol CO x

43.9kJ

=
21.95kJ

2 mole CO

4.

When water is formed from hydrogen gas and oxygen gas, 1.61 kJ/ g H
2
O of
energy is released.

a.

What the heat released per mole o
f water?

1.61kJ

x

18.01g H
2
O

=
29.0kj/mole

H
2
O

g H
2
O 1 mole H
2
O

b.

Is the reaction exothermic or endothermic?

exothermic

c.

Write the thermochemical equation (reaction including the heat)

2 H
2

(g) + O
2

(g)

㈠2
2
O (g) + 58.0k
J

(
2 moles H
2
O x 29.0kJ/ mole
)

d. In the formation of 150.0g of water, how much energy would be evolved?

150.0g H
2
O x

1 mole H
2
O

x

58.0kJ

=
241.5kJ

18.01g H
2
O

2 mole H
2
O

Assignment 4:

Thermoche
mical Reactions and Calculating
the Heat of Reaction
(

H or Change in 䕮瑨alpy)
.

1.

A 2.5 g sample of Mg is placed in 150.0 mL of HCl. The temperature of the
water increased from 15.0
o
C to 45.0
o
C.

Calculate the total heat released in the reaction.

q = 150.0g x 4.18

j

x 30.0
o
C = 18810j

g
o
C

Calculate the number of moles of Mg.

2.5g Mg x

1 mole Mg

= .10 mole Mg

24.3g Mg

Calculate the

H (
heat per mole of Mg
)
.

18810j

=

x joules

x =
-
188100j or

-
190kJ

0.10 mol Mg 1 mol Mg

Is the reaction exothermic or endothermic?

exothermic

Write the
thermochemical equation (
equation including the heat released
)
.

Mg (s) + 2 HCl (aq)

M权l
2

(aq) + H
2

(g) + 190kJ

2.

If 21 g of propane is burned under 150.0 g of water, the temperature of the water
increases from 21.0
o
C to 21.6
o
C.

What is the heat released by this process?

q = 150.0g x 4.18

j

x 0.6
o
C = 376.2j

g
o
C

How many moles of propa
ne burned?

21g C
3
H
8

x

1 mole C
3
H
8

= 0.476 moles

44.094g C
3
H
8

What is the heat per mole (Molar Heat of Combustion or

H) for propane?

376.2 joules

=

x joules

=
-
790j

0.476 mole C
3
H
8

1 mole C
3
H
8

Write the react
ion for the combustion of propane showing the heat.
(thermochemical equation)

C
3
H
8

(g) + 5 O
2

(g)

㌠3O
2

(g) + 4 H
2
O (g) + 790j

Assignment 5:

Calculating

H

wi瑨 Hea琠o映Forma瑩on Chart
.

Calculate the

H for each of the following reactions:

CaO (s) + CO
2

(g)

CaCO
3

(s)

2 C
2
H
2

(g) + 5 O
2

(g)

4 CO
2

(g) + 2 H
2
O (g)

2 NH
3

(g)

N
2

(g) + 3 H
2

(g)

2 HNO
3

(l)

N
2
O
5

(g) + H
2
O (g)

SO
3

(g) + H
2
O (g)

H
2
SO
4

(l)

2 Na (s) + 2 HCl (g)

2 NaCl (s) + H
2
O (l)

HNO
3

(l) + NaOH (s)

NaNO
3

(s) H
2
O (l)

Na
2
SO
4

(s) + 10 H
2
O (l)

Na
2
SO
4

* 10 H
2
O (s)

TiCl
4

(l) + 2 H
2
O (l)

TiO
2

(s) + 4 HCl (g)

NH
4
Cl (s)

NH
3

(g) + HCl (g)

Assignment 6:

Calculating

H

with Hess’ Law
.

Assignment 7:

Thermochemical Equations.

2 H
2
O
2

(aq)

㈠2
2
O (l) + O
2

(g) + 108 kJ

Is the reaction exothermic or endothermic?

exothermic

What is the

H

got the reaction?

-
108 kJ

Whi
ch has more energy, the products or the reactants?
R
eactants have more energy

How much energy is released when 56.0g of H
2
O
2

decomposes?

56.0g x

1mol H
2
O
2=

x

108kJ

=
8
8.
9 kJ released

34.02g H
2
O
2

2

mol H
2
O
2

N
2
H
4

(g)

+ O
2

(g)

N
2

+ H
2
O (l)

H

-
㘲㜮㘠kJ

Write the thermochemical equation.

N
2
H
4

(g) + O
2

(g)

N
2

+ H
2
O (l) + 627.6 kJ

Is the reaction exothermic or endothermic?
exothermic

Will it feel hot or cold?
hot

Which has more energy, the reactant or products? Show graph

with energy.
Reactants

How much energy is released when 82.0g of N
2
O
4

is reacted?

82.0g N
2
O
4

x

1 mole N
2
H
4

x

627.6 kJ

=
1700 kJ
(2 sig fig)

30.03g N
2
H
4

1 mole N
2
H
4

CaCO
3

(s)

C慏 (s) † † O
2

(g)

H

=‫4
㈮㔠kc慬

Write the thermochemical equation.

42.5 kcal + CaCO
3

(s)

C慏 (s)†‫†⁃O
2

(g)

Is the reaction exothermic or endothermic?
endothermic

Which has more energy, the reactants or the products?
Products have more energy

How much energy is
(absorbed or released) when 501.0g of CaCO
3

decomposes?

501.0g CaCO
3

x

1 mol CaCO
3

x

42.5 kcal

=
213 kcal absorbed

100.09g CacO
3

1 mol CaCO
3

Would this reaction tend to be spontaneous (happen)? Why?
No, it is endotherm
ic and so
not favorable in terms of energy change.

Assignment 8:

Thermochemical Equations.

Solid sulfur combines with oxygen gas to form sulfur dioxide gas. The

H

re慣ti潮 is
-
㈹㜠2J

Write the thermochemical equation for the reaction.

S (s)

+ O
2

(g)

2

+ 297 kJ

Which has more energy, the reactants or the products?
Reactants

Is the reaction exothermic or endothermic?
Exothermic

Would it feel hot or cold?
Hot

How much sulfur dioxide will be formed when 400.0 kJ of energy is

released?

400.0kJ x

1 mol SO
2

x

64.064g SO
2

=
86.3g SO
2

297 kJ 1 mol SO
2

How much energy is released when 82.0g of sulfur reacts?

82.0g S x

1 mol S

x

297 kJ

=
759 kJ

released

32.07g S 1mol S

Ethyne gas (C
2
H
2
) reacts with oxygen gas in a combustion reaction and produces
2512 kJ of energy per mole of ethyne.

Write the thermochemical equation.

C
2
H
2

(g) + 2 ½ O
2

(g)

㈠2O
2

(g) + H
2
O (g) + 2512 kJ

What
is the

H

for the reaction?
-
2512 kJ

Is the reaction exothermic or endothermic? Show graph with energy.
exothermic

Would this reaction tend to be spontaneous (happen) in terms of energy change?
Yes
, it is exothermic as so is favorable in terms of ene
rgy change. Systems tend
toward lower energy.

How much energy is released when 25.0g of ethyne reacts?

25.0g C
2
H
2

x

1 mol C
2
H
2

x

2512 kJ

=
2410 kJ released

26.04g C
2
H
2

1 mol C
2
H
2

How much ethyne was burned if 4001 kJ of ener
gy was released?

4001 kJ x

1 mol C
2
H
2

x

26.04g C
2
H
2

=
41.48g C
2
H
2

2512 kJ

1 mol C
2
H
2

Assignment 9:

Thermochemical Equations
.

Methane (CH
4
) undergoes combustion.

1.

Use the heat of formation chart to calculate the

H

for the reaction.

CH
4

(g) + 2 O
2

(g)

CO
2

(g) + 2 H
2
O (g)

1(
-
17.889kcal) + 2(0kcal) 1(
-
94.0518kcal) + 2(
-
57.7979kcal)

=

-
17.889kcal

=
-
209.6476kcal

-
209.6476kcal

(
-
17.889kcal) =
-
192kcal

2.

Write the thermochemical equation.

CH
4

(g) + 2 O
2

(g)

2

(g) + 2 H
2
O (g) + 192kcal

3.

Is the reaction exothermic or endothermic?
exothermic

4.

Which has more energy, reactants or products? Draw a graph to show the energy
relation
ships on the reaction.
Reactants have more energy!

5.

How many grams of methane are needed to produce 4000.0 kcal of energy?

4000.0kcal x

1 mol CH
4

x

16.05g

=
334kcal

192kcal 1 mol CH
4

6.

How much heat is relea
sed per gram of methane?

192kcal

=
12.0kcal/g

16.05g CH
4

7.

Would you expect this reaction to be spontaneous at room temperature? What is
the driving force?

The change in enthalpy is very favorable (a large negative number)
bec
ause the reaction is very exothermic. The change in entropy is
probably not significant as it goes from all gases to all gases. So, Gibbs
Free Energy is probably negative and the reaction is spontaneous.

Calculate the enthalpy change
(

H
)⁦潲 the re慣ti潮 in which s潬id 慬uminum re慣ts
with s潬id ir潮(III) 潸ode t漠or潤uce s潬id ir潮 慮d s潬id 慬uminum 潸ode.

Gi癥n:

㈠2l (s)† †
㌯㈠2
2

(g)

2
O
3

(s)

H

-
ㄶ〱1kJ

㈠2e s)† †㌯㈠2
2

(g)

2
O
3

(s)

H =
-
㠲ㄠkJ

flip:

Fe
2
O
3

(s)

2 Fe +
3/2 O
2

(g)

H = +821 kJ

Al (s) + Fe
2
O
3

(s)

Fe (s) + Al
2
O
3

(s)

H =
-
786 kJ

1.

Write the thermochemical equation.

Al (s) + Fe
2
O
3

(s)

Fe s) † † l
2
O
3

(s) + 786 kJ

2.

Is the reaction exothermic or endothe
rmic?
exothermic

3.

Would the reaction get hot or cold?
Hot

4.

Which has more energy, reactants or products? Draw a graph to show the energy
relationships on the reaction.
The
Reactants

have more energy.

5.

How many grams of iron(III) oxide are neede
d to produce 4000.0 kJ of energy?

4000.0 kJ x

1 mol Fe
2
O
3

x

159.689g Fe
2
O
3

=
813
g

786 kJ

1 mol Fe
2
O
3

6.

How much heat is released per gram of aluminum?

786 kJ

=
29.1 kJ/g Al

26.98g Al

7.

Would you expect th
is reaction to be spontaneous at room temperature? What is
the driving force?

The change in enthalpy is very favorable (a large negative number) because the
reaction is very exothermic. The change in entropy is probably not signi
ficant as
it goes from al
l solids to all solids
. So, Gibbs Free Energy is probably negative
and the reaction is spontaneous.

Calculate the heat of reaction for the following:

2 C (graphite) + H
2

(g)

C
2
H
2

(g)

given:

x4:

4
C (graphite) +
4
O
2

(g)

4

2

(g)

H

-
㌹㌮㔠k䨠

H

-
ㄵ㜴⸰

2
H
2

(g) +
1

O
2

(g)

2
H
2
O (l)

H =
-
㈸㔮㠠kJ

H

-
㔷ㄮ5

㈠2
2
H
2

(g) + 5 O
2

(g)

㐠4O
2

(g) + 2 H
2
O (l)

H =
-
㈵㤸⸸2kJ

flip:

㐠4O
2

(g) + 2 H
2
O (l)

㈠C
2
H
2

(g) + 5

O
2

(g)

H =‫㈵㤸⸸2kJ

4

C (杲慰hite) ‫†

H
2

(g)

C
2
H
2

(g)

H

=‫㐵㌮4

C (杲慰hite) ‫†

H
2

(g)

C
2
H
2

(g)

H

=‫㈲㘮2

Evaluate this reaction in terms of

H
,

S, and

G.

The

H is positive, so not favorable.

The

S is pr
obably positive, but only marginally as it goes from one solid and one
gas to only one gas. This is favorable as it is an increase in entropy.

So

G is negative at higher temperatures.

Do you think this reaction would be spontaneous?

The change in e
nthalpy is

unfavorable (a positive

number) because

the reaction is
endothermic
. The change
in entropy is probably positive as it ends with only
gases
. S
o, Gibbs Free Energy is

negative
at higher temperatures.