Download AP Chemistry 2015-2016 Name: Chapter 5: Thermodynamics Date

AP Chemistry 2015-2016
Chapter 5: Thermodynamics
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5.1-5.4 Thermodynamic Basics
1) Define and describe the following thermochemistry terms:
a) Energy
Helpful Information:
w = -P∆V
b) Work
c) Heat
101 J = 1 atm ∙ L
PV = nRT (Ideal Gas Law)
R values listed on your cheat sheet
d) Kinetic energy
STP – standard conditions
25°C
e) Potential energy
f) Joule
1 atm of pressure
∆E = q + w
g) System
h) Surroundings
i) Internal energy
j) Endothermic
k) Exothermic
l) State function
2) Thoroughly explain this equation for electrostatic potential energy: Eel = kQ1Q2
including each letter or symbol.
d
3) Describe the First Law of Thermodynamics.
4) The First Law of Thermodynamics can be quantitatively summarized by the equation: ∆E = q + w
a) What does q represent?
b) What does w represent?
c) Under what conditions will the quantities q and w be negative numbers? Discuss each separately.
5) Calculate ∆E and determine if the process is endothermic or exothermic for the following cases:
WATCH YOUR UNITS!!
a) A system absorbs 85 kJ of heat from its surroundings while doing 29 kJ of work on the
surroundings.
b) q = 1.50 kJ and w = –657 J
c) The system releases 57.5 kJ of heat while doing 13.5 kJ of work on the surroundings.
6) Calculate ∆E for each of the following cases:
a) q = + 51 kJ, w = - 15 kJ
b) q = + 100. kJ, w = - 65 kJ
c) q = - 65 kJ, w = - 20 kJ
d) In which of these cases does the system do work on the surroundings?
7) Calculate ∆E for each of the following:
a) q = - 47 kJ, w = + 88 kJ
b) q = + 82 kJ, w = + 47 kJ
c) q = + 47 kJ, w = 0
d) In which of these cases do the surroundings do work on the system?
8) A system releases 125 kJ of heat while 104 kJ of work is done on the system. Calculate the change in
internal energy (in kJ).
9) A system undergoes a process consisting of the following two steps:
Step 1: The system absorbs 73 J of heat while 35 J of work is done on it.
Step 2: The system absorbs 35 J of heat while performing 72 J of work.
Calculate the change in internal energy for the overall process (in J).
10) The volume of an ideal gas is decreased from 5.0 L to 5.0 mL at constant pressure of 2.0 atm.
Calculate the work associated with this process (in J). WATCH YOUR UNITS!!!
11) The reaction of nitrogen with hydrogen to make ammonia is
N2 (g) + 3H2 (g) 2HN3 (g)
ΔH = -92.2 kJ
What is the value of ΔE (in kJ) if the reaction is carried out at a constant pressure of 40.0 atm and the
volume change is -1.12L? WATCH YOUR UNITS!!!
12) A strip of magnesium of mass 15 g is dropped into a beaker of dilute hydrochloric acid. What work is
done on the surrounding atmosphere (1.00 atm pressure, 25°C) by the subsequent reaction?
13) Calculate the work done (in joules) by a chemical reaction if the volume increases from 3.2 L to 3.4 L
against a constant external pressure of 3.6 atm. What is the sign of the energy change?
14) When solutions containing silver ions and chloride ions are mixed, silver chloride precipitates:
Ag+(aq) + Cl–(aq) → AgCl(s) ∆H = –65.5 kJ
a) Calculate ∆H for the formation of 2.00 mol of AgCl.
b) Calculate ∆H for the formation of 2.50 g of AgCl
15) You are given ∆H for a process that occurs at constant pressure. What additional information is
needed to determine ∆E for the process?
16) A gas is confined to a cylinder with a piston under constant atmospheric pressure (fig. 5.3). When the
gas reacts, it releases 79 kJ of heat to its surroundings and does 18 kJ of P-V work on its surroundings.
What are the values for ∆H and ∆E for this process?
17) The thermochemical equation for the burning of one mole of benzene under standard conditions is
C6H6(l) + 15/2 O2(g) → 6 CO2(g) + 3 H2O(l) ∆H comb = –3267.7 kJ
a. Is this reaction exothermic or endothermic? How do you know?
b. How much heat is released when a 5.00-g sample of benzene is burned in excess oxygen under
standard conditions? (m.w. C6H6 = 78.11 g/mol)
18) Used in welding metals, the reaction of acetylene with oxygen:
C2H2(g) + 5/2 O2(g) →H2O(g) + 2 CO2(g)
∆H=–1255.5 kJ
How much PV work is done (in kilojoules) and what is the value of ∆E (in kilojoules) for the reaction of
6.50 g of acetylene at atmospheric pressure if the volume change is –2.80 L?
19) Aluminum metal reacts with chlorine with a spectacular display of sparks:
2 Al(s) + 3 Cl2(g) →2 AlCl3(s)
∆H= –1408.4 kJ
How much heat (in kilojoules) is released on reaction of 5.00 g of Al?
5.5: Calorimetry
1. Water has a specific heat capacity of 4.184 J/g·°C.
This means it takes 4.184 J to heat 1.00 gram of water 1.00°C.
a) How much energy will it take to heat 10.0 grams of water 1°C? ______________
b) How much energy is needed to heat 30.0 g H2O from 10.0 °C to 50.0 °C? ____________
2.
Let’s try a standard calorimetry problem.
A pot of water (2.5 Liters of water) initially at 25.0C is heated to boiling (100.°C).
How much energy (in J) is needed to heat the water? (The density of water is 1 g/mL.)
What would this amount of heat be in kJ? ___________
3.
What amount of heat is released when 175 g of water cools from 100.°C to room temperature, 20.0
°C?
4.
We don’t always have to warm up or cool down water. The specific heat capacity of copper metal is
0.39 J/g·°C. It is _____________ (easier/more difficult) to heat up copper than to heat up water.
How much energy would it take to heat up a 5.20 g sample of copper from 20.0 °C to 100.°C?
5.
If 300. J of heat energy were used to heat up a 5.00 gram sample of copper metal and a 5.00 gram
sample of water both starting at 10.0°C, calculate the final temperature of each sample?
Signs of T and q:
 q means heat is released. + q means heat is absorbed.
T is always final temperature – initial temperature.
If something is getting hotter (10°  30°) the T is 30 – 10 = + 20°. (heat is absorbed)
If something is getting cooler (75°  25°) the T is 25 – 75 =  50°. (heat is released)
6.
Suppose we mix 90.0 grams of hot water (90.0°C) with 10.0 grams of cold water (10.0°C).
Let x = the final temperature. C = 4.184 J/g·C
a. Set up an expression for the energy released (q) by the hot water (qhot = mhotCThot)
b. Set up an expression for the energy absorbed (q) by the cold water (qcold = mcoldCTcold)
c. Knowing that the heat released =  heat absorbed, combine the two expressions and solve for x.
7.
We don’t always have to use water. Let’s use some aluminum shot (pellets). 175 grams of hot
aluminum (100.°C) is dropped into an insulated cup that contains 40.0 mL of ice cold water (0.0°C).
Follow the example above to determine the final temperature, x.
a. Set up an expression for the heat lost by the aluminum (C=0.900 J/g·°C)
b. Set up an expression for the heat gained by the cold water.
c. Put the two expressions together (don’t forget to change one of the signs) and solve for x.
8.
Somewhat Confusing Definitions:
There are several terms used in this chapter that sound very similar. Use the data provided to
calculate each of them to clarify the differences. I’ve added some “Notes” that I hope will help.
74.8 J of heat is required to raise the temperature of 18.69 g of silver from 10.0C to 27.0C.
a. What is the heat capacity of the silver sample? (J/C)
Note: This is a useful value only for this specific sample of silver.
b. What is the specific heat capacity of silver? (J/g·C)
Note: This is a useful value for any sample of silver that is heated or cooled. This is equivalent to
the 4.184 J·g-1·°C-1 that we use for water. This value is also called the specific heat.
5.6-5.7: Hess’s Law and Enthalpies of Formation
Use standard enthalpies of formation (appendix C) to determine the change in enthalpy for each
reaction
a) NaOH(s) + HCl(g) ----> NaCl(s) + H2O(g)
b) 2 CO(g) + O2(g) ---> 2 CO2(g)
c) CH4(g) + 2 O2(g) ---> CO2(g) + 2 H2O(l)
d) 2 H2S(g) + 3 O2(g) ---> 2 H2O(l) + 2 SO2(g)
e) 2 NO(g) + O2(g) ---> 2 NO2(g)
1. Using standard enthalpies of formation, calculate the standard enthalpy change for the combustion of
1 mol benzene, C6H6(l), to CO2 (g) and H2O (l).
2. Using standard enthalpies of formation, calculate the enthalpy change for the combustion of 1 mol of
ethanol: C2H5OH (l) + 3O2 (g) → 2CO2 (g) + 3H2O (l)
3. The standard enthalpy change for the reaction CaCO3(s) → CaO(s) + CO2(g) is 178.1 kJ. From the
values for the standard enthalpy of formation of CaO(s) and CO2(g), calculate the standard enthalpy of
formation of CaCO3(s).
4. Given the following standard enthalpy of reaction, use the standard enthalpies of formation to
calculate the standard enthalpy of formation of CuO(s):
CuO(s) + H2(g) → Cu(s) + H2O(l)
ΔH° = -129.7 kJ
5. Using Hess’s Law, calculate the standard enthalpy of formation of gaseous diborane (B2H6) using the
following thermochemical information:
4B(s) + 3O2(g) → 2B2O3(s)
2H2(g) + O2(g) → 2H2O(l)
B2H6(g) + 3O2(g) → B2O3(s) + 3H2O(l)
ΔH = -2509.1 kJ
ΔH = -571.7 kJ
ΔH = -2147.5 kJ
6. Naphthalene (C10H8) is a solid aromatic compound often sold as mothballs. The complete
combustion of this substance to yield CO2(g) and H2O(l) at 25° C yields 5154 kJ/mol.
a) Write balanced equations for the formation of naphthalene from the elements and for its combustion.
b) Calculate the standard enthalpy of formation of naphthalene.
7.
Iron ore can be converted to iron metal with CO gas.
FeO (s)  CO (g)  Fe (s)  CO2 (g)
Calculate the standard enthalpy change for this reaction from these reactions
of iron oxides with CO :
(1) 3 Fe2O3 (s)  CO (g)  2 Fe3O4 (s)  CO2 (g)
H  - 47 kJ
(2) Fe2O3 (s)  3 CO (g)  2 Fe (s)  3 CO2 (g)
H  - 25 kJ
(3) Fe3O4 (s)  CO (g)  3 FeO (s)  CO2 (g)
H  19 kJ
8. Calculate ΔH for the reaction C2H4 (g) + H2 (g) → C2H6 (g), from the following data.
C2H4 (g) + 3 O2 (g) → 2 CO2 (g) + 2 H2O (l)
ΔH = -1411. kJ/mole
C2H6 (g) + 7/2 O2 (g) → 2 CO2 (g) + 3 H2O (l)
ΔH = -1560. kJ/mole
H2 (g) + ½ O2 (g) → H2O (l)
ΔH = -285.8 kJ/mole
9. Calculate ΔH for the reaction 4 NH3 (g) + 5 O2 (g) → 4 NO (g) + 6 H2O (g), from the following data.
N2 (g) + O2 (g) → 2 NO (g)
ΔH = -180.5 kJ
N2 (g) + 3 H2 (g) → 2 NH3 (g)
ΔH = -91.8 kJ
2 H2 (g) + O2 (g) → 2 H2O (g)
ΔH = -483.6 kJ
I can…
 state the sign of H based on observation of warming or cooling of the surroundings.
 correctly apply the terms exothermic and endothermic to situations where the surroundings are
warming or cooling.
Measuring Heat
 state the units of heat capacity, specific heat, and molar heat capacity as well as the significance of each.
 use calorimetry (q=mCT) to calculate heat changes during temperature changes.
 calculate the heat transferred when two objects, at different temperatures, come into contact.
Energy = Heat and Work
 state the difference between work and heat energy.
 state the difference between system and surroundings.
 recognize the system and the surroundings in a chemical or physical system.
 calculate the change in internal energy based on changes in heat absorbed by the system and work
done by the system.
 state that H is a more general (and useful) measure of energy than E and that H = q when a reaction
occurs at constant pressure.
Chemical Work = Expanding Gases
 relate physical work (w=F·d) and chemical work (w=-P·V).
 calculate PV work done by an expanding gas.
 state that no work is done in a constant volume situation such as a bomb calorimeter.
Calculating H -- Hess’s Law
 state the definition of a state function.
 list examples of properties that are and are not state functions.
 write the equation for the heat of formation of a substance.
 state that the heat of formation of an element under standard conditions has a value of zero.
 use Hess’s Law to calculate the energy of a chemical or physical change.
C2H2(g) + 2 H2(g) -> C2H6(g)
Information about the substances involved in the reaction represented above is summarized in the
following tables.
Substance
DH°f
(kJ/mol)
C2H2(g)
226.7
C2H6(g)
-84.7
(a)
Write the equation for the heat of formation of C2H6(g)
(b)
Use the above information to determine the enthalpy of reaction for the equation given.
C6H5OH(s) + 7 O2(g) -> 6 CO2(g) + 3 H2O(l)
When a 2.000-gram sample of pure phenol, C6H5OH(s), is completely burned according to the equation
above, 64.98 kilojoules of heat is released. Use the information in the table below to answer the questions
that follow.
Standard Heat
of Formation,
Substance
DH°f; at 25°C
(kJ/mol)
CO2(g)
-393.5
H2O(l)
-285.85
C6H5OH(s)
?
(a) Calculate the molar heat of combustion of phenol in kilojoules per mole at 25°C.
(b) Calculate the standard heat of formation, DH°f, of phenol in kilojoules per mole at 25°C.
1.
How many joules are equivalent to 37.7 cal?
a) 9.01 J
c) 1.51 J
b) 4.184 J
d) 158 J
2.
The quantity of heat that is needed to raise the temperature of a sample of a substance 1.00 degree is
called its
a) heat capacity
c) enthalpy
b) specific heat
d) kinetic energy
3.
Equal masses of two substances, A & 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 specific heat of A is double that of B.
b) the specific heat of B is double that of A.
c) the specific heat of B is negative.
d) the specific heat of B is triple that of A.
4.
If 25 J are required to change the temperature of 5.0 g of substance A by 2.0C, what is the specific
heat of substance A?
a) 250 J/gC
c) 10. J/gC
b) 63 J/gC
d) 2.5 J/gC
5. How much energy is required to change the temperature of 2.00 g aluminum from 20.0C to 25.0C?
The specific heat of aluminum is 0.902 J/gC.
a) 2.3 J
c) 0.36 J
b) 9.0 J
d) 0.090 J
6.
Consider the thermal energy transfer during a chemical process. When heat is transferred to the
system, the process is said to be _______ and the sign of H is ________.
a) exothermic, positive
c) exothermic, negative
b) endothermic, negative
d) endothermic, positive
7.
What is the E for a system which has the following two steps:
Step 1: The system absorbs 60 J of heat while 40 J of work are performed on it.
Step 2: The system releases 30 J of heat while doing 70 J of work.
a) 100 J
c) 30 J
b) 90 J
d) zero
8.
When two solutions react the container “feels hot.” Thus,
a) the reaction is endothermic.
b) the reaction is exothermic.
c) the energy of the universe is increased.
d) the energy of both the system and the surroundings is decreased.
9.
The equation for the standard enthalpy of formation of N2O3 is
a) N2O(g) + O2(g)  N2O3(g)
b) N2O5(g)  N2O3(g) + O2(g)
c) NO(g) + NO2(g)  N2O3(g)
d) N2(g) + 3/2 O2(g)  N2O3(g)
10. For the general reaction
2 A + B2  2 AB,
H is +50.0 kJ.
We can conclude that
a) the reaction is endothermic.
b) the surroundings absorb energy.
c) the standard enthalpy of formation of AB is -50.0 kJ.
d) the molecule AB contains less energy than A or B2.
11. Calculate the enthalpy of combustion of C3H6 [C3H6(g) + 9/2O2(g)  3CO2 + 3H2O] using the following:
3C(s) + 3H2(g)  C3H6(g)
H= 53.3 kJ
C(s) + O2(g)  CO2(g)
H=-394 kJ
1
H2(g) + /2O2(g)  H2O(l)
H=-286 kJ
a) -1517 kJ
c) -626 kJ
b) 1304 kJ
d) -2093 kJ
12. Which one of the following would have an enthalpy of formation value (Hf) of zero?
a) H2O(g)
c) H2O(l)
b) O(g)
d) O2(g)
13.
Calculate the heat of vaporization of titanium (IV) chloride: TiCl4(l)  TiCl4(g) using the following
enthalpies of reaction:
Ti(s) + 2Cl2(g)  TiCl4(l) H=-804.2 kJ
TiCl4(g)  2Cl2(g) + Ti(s) H= 763.2 kJ
a) -1567 kJ
c) 1165 kJ
b) -783.7 kJ
d) 41 kJ
14. Calculate the enthalpy of reaction for D + F  G + M using the following equations and data:
G+CA+B
H = +277 kJ
C+FA
H = +303 kJ
DB+M
H = -158 kJ
a) -132 kJ
c) +422 kJ
b) -422 kJ
d) +132 kJ
15. Calculate the standard enthalpy of the reaction for the process 3NO(g)  N2O(g) + NO2(g) using the
standard enthalpies of formation (in kJ/mol): NO = 90; N2O = 82.1; NO2 = 34.0
a) -153.9 kJ
c) -26.1 kJ
b) 206 kJ
d) 386 kJ
16. The standard molar enthalpy of combustion is -1277.3 kJ for the combustion of ethanol.
C2H5OH(l) + 3O2(g)  2CO2(g) + 3H2O(g)
Calculate the standard molar enthalpy of formation for ethanol based on the following standard
enthalpies of formation:
Hf CO2 = -393.5 kJ/mol
Hf H2O = -241.8 kJ/mol
a) -642.7 kJ/mol
c) 235.1 kJ/mol
b) -235.1 kJ/mol
d) 642.7 kJ/mol
17.
Calculate the amount of heat needed to change 25.0 g ice at 0C to water at 0C.
The heat of fusion of H2O = 333 J/g;
a) 56.5 kJ
c) 7.06 kJ
b) 8.33 kJ
d) 463 kJ
1.
If the temperature of a 50.0-gram block of aluminum increases by 10.9 K when heated by 500
Joules, calculate the
a.
heat capacity of the aluminum block
b.
specific heat of aluminum
2.
Calculate the heat necessary to change the temperature of one kg of iron from 25C to 1000C.
The specific heat of iron is 0.451 JK-1g-1.
3.
If a 40 gram block of copper at 100C is added to 100 grams of water at 25C, calculate the final
temperature assuming no heat is lost to the surroundings. The specific heat of copper is 0.385 JK1g-1 and the specific heat of water is 4.184 JK-1g-1.
4.
Calculate the amount of heat needed to melt 27.0 g of ice if the heat of fusion of ice is 6.009 kJ/mol.
5.
If 27.0 grams of ice at 0C is added to 123 grams of water at 100C in an insulated container,
calculate the final temperature. Assume that the specific heat of water is 4.184 JK-1g-1.
6.
A 50 gram block of an unknown metal alloy at 100C is dropped into an insulated flask containing
approximately 200 grams of ice. It was determined that 10.5 grams of the ice melted. What is the
specific heat capacity of the unknown alloy?
7.
If the enthalpy change for the combustion of propane is –2220 kJ/mole propane, what quantity of
heat is released when 1 kg of propane is burned?
C3H8(g) + 5O2(g)  3CO2(g) + 4H2O(l)
H-2220 kJ
8.
Using the following thermochemical data, calculate the molar heat of combustion, Hcombustion of
methane, CH4:
2CH4(g) + 3O2(g)  2CO(g) + 4H2O(l)
H = -1215 kJ
2C(s) + O2(g)  2CO(g)
H = -221 kJ
C(s) + O2(g)  CO2(g)
H = -394 kJ
9.
Calculate the standard molar enthalpy of formation of methane from the data given in question 8,
your answer to question 8, and the following:
Hf (H2O(l)) = -286 kJ/mol
10.
When ammonia is oxidized to nitrogen dioxide and water, the quantity of heat released equals 349
kJ per mol of ammonia:
2NH3(g) + 7/2O2(g)  2NO2(g) + 3H2O(l)
H = -698 kJ
Calculate the standard molar enthalpy of formation of ammonia if
Hf (H2O(l)) = -286 kJ/mol
Hf (NO2(g)) = +33 kJ/mol
11.
When 40 grams of ammonium nitrate is dissolved in 100 grams of water in a constant-pressure
coffee-cup calorimeter, the temperature of the solution drops by 22.4C. If the specific heat of the
solution is 4.18 JK-1g-1, calculate the enthalpy of solution of ammonium nitrate.