Download formulas are found on table t

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Name _____________________________
Mrs. Murray
Chemistry, period____
Date ______________
UNIT 9: Thermodynamics
Text Book Chapter 15: Energy and Chemical Change, pages 514-547
A. Heat / Enthalpy Calculations. Show all work.
1. How much heat energy is required to raise 150 grams of water from 20 C to 30 C? Express your
answer in Joules and kiloJoules.
2. The temperature of 50 grams of water is raised to 50 C, by the addition of 1,000 Joules of heat
energy. What was the initial temperature of the water?
3. How much heat energy is released when 50 grams of water freezes? Express your answer in Joules
and kiloJoules.
4. How much heat is given off when a 400 gram sample of aluminum cools from 600C to 25 C? (Cp of
aluminum is 0.9 J/g C)? Express your answer in Joules and kiloJoules.
5. How much heat is given off when 150 grams of water cools from 85 C to 40 C? Express your
answer in Joules and kiloJoules.
6. A sample of water is heated from 10 C to 25 C by the addition of 30 kJ of heat. What is the mass of
the water? Express your answer in grams and kilograms.
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B. Heat / Enthalpy Calculations. Show all work.
1. How much energy is absorbed when 250 grams of ice melts?

Is this an exothermic or endothermic process?

What happens to kinetic and potential energy during this phase change?

How much energy would be released when 250 grams of water freeze?
2. How much energy is absorbed when 250 grams of water boil?

Is this an endothermic or exothermic process?

What happens to kinetic and potential energy during this phase change?

How much energy would be released when 250 grams of water vapor condense?
3. Is it easier to melt ice or boil water? Explain your answer.
C. Reference Table I Worksheet
1. Which reaction is most endothermic? Write the reaction including the H value.
2. Write the reaction for the synthesis of ammonia. Write the reaction including the H value. Is this
reaction endothermic or exothermic?
3. Which reaction is most exothermic? Write the reaction including the H value.
4. Write the reaction for the dissolving of KNO3 in water. Write the reaction including the H value. Is
this reaction endothermic or exothermic?
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5. How much energy is produced when 3 moles of LiBr dissolve in water? ________________
6. How much energy is absorbed when 1 mole of NO2 is formed from it’s elements? ________
7. How much energy is absorbed when 2 moles of potassium nitrate dissolve? ____________
8. Would the solution in #7 feel cold or warm to the touch? Explain. _____________________
_________________________________________________________________________
9. How much energy is released when 4 moles of ammonia are formed? _________________
10. Would the solution in #9 feel cold or warm to the touch? Explain. _____________________
_________________________________________________________________________
11. How much energy is absorbed when 0.5 moles of hydrogen iodide is formed? __________
D. Potential Energy Diagrams
1. What is the energy of the reactants for the forward reaction?
2. What is the energy of the products for the forward reaction?
3. Is the forward reaction endo or exothermic? Calculate the
value of H for this reaction.
4. Is the reversed reaction endo or exothermic? Calculate the
value of H for this reaction.
5. What is the value of the activated complex?
6. Calculate the activation energy for the forward reaction.
7. Calculate the activation energy for the reverse reaction.
8. Potential energy of the products______________
9. Potential energy of the activated complex ___________
10. Potential energy of the reactants __________
11. Activation energy ___________
12. Heat of reaction ___________
13. Endo or exothermic? _____________
14. Activation energy for the reverse reaction ____________
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15. Heat of reaction for the reverse reaction __________
E. More Potential Energy Diagrams
1. Is the reaction endothermic or exothermic?
_________________
2. What number(s) represents the potential energy of the
reactants? __________
3. What number(s) represents H? __________
4. What number(s) represents the activation energy for the
reaction? ___________
5. What number(s) represents the activated complex?
______________
6. What number(s) represents heat of reaction for the reverse reaction? ____________
7. What number(s) represents the potential energy of the products? __________
8. What number(s) represents the difference between the activation energy for the forward reaction and
the activation energy of the reverse reaction? ____________
F. Heat Questions
Base your answers to questions 1 and 2 on the heating curve below, which represents a substance
starting as a solid below its melting point and being heated at
a constant rate over a period of time.
1. What is happening to the average kinetic energy of the
particles during segment BC?
2. How does this heating curve illustrate that the heat of
vaporization is greater than the heat of fusion?
3. The letter B represents which chemical formula or formulas in
the equation?
4. If 682.2 kilojoules are absorbed, how many moles of C2H2(g)
are produced?
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In a laboratory experiment, 10.00 grams of an unknown solid is added to 100.0 milliliters of water and the
temperature of the resulting solution is measured over several minutes, as recorded in the table below.
5. On the grid provided, mark an appropriate scale on the axis labeled
“Temperature (°C).” An appropriate scale is one that allows a trend to be
seen.
6. Plot the data from the data table. Circle and connect the points.
0
1
2
3
4
time (minutes)
7. Given the statement:
The unknown solid is either sodium hydroxide or lithium bromide, and both of these compounds dissolve
in water exothermically.
a Explain how the experimental data support the statement.
b State specific information from Reference Table I to support the statement.
G. Entropy
1. Define entropy in your own words.
2. Does entropy increase or decrease with increase in temperature? Explain.
3. Which member of the following pairs has the greater predicted amount of entropy.
a. CO2 (g) or CO2 (s)
c. FeCl2 (s) or FeCl3(s)
b. H2O (l) or H2O (s)
d. Fe(s) at 25°C or Fe(s) at 100°C
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4. For each of the following reactions, indicate whether you would expect the entropy of the system to
increase or decrease, and explain why.
a. CH3OH(l)  CH3OH(g)
h. 2 HgO(s) → 2 Hg(l) + O2(g)
b. N2O4(g)  2NO2(g)
i. Ba+2(aq) + SO4 -2(aq) → BaSO4(s)
c. 2KClO3(s)  2KCl(s) + 3O2 (g)
j. 2H2O2(l) → 2 H2O(l) + O2(g)
d. 2NH3(g) + H2SO4(aq)  (NH4)2SO4(aq)
k. 2 SO2(g) + O2(g) → 2 SO3(g)
e. 2 N2(g) + O2(g) → 2 N2O(g)
l. MgO(s) + CO2(g) → MgCO3(s)
f. CaCO3(s) → CaO(s) + CO2(g)
m. PCl5(s) → PCl3(l) + Cl2(g)
g. Zn(s) + 2 HCl(aq) → ZnCl2(aq) + H2(g)
H. Gibbs Free Energy
Formula
G = __________________
Free energy determines whether a reaction occurs spontaneously. If G is ___________(+/-), the
reaction is spontaneous, if it is __________(+/-) the reaction is not spontaneous.
Reactions that are _____________( exo/endo) favor spontaneity. Spontaneity is also favored when
particles ______________ (increase/decrease) entropy.
G is negative when H is ____________(+/-) and S is __________(+/-).
For the reaction:
2H2 (g) + 1 O2 (g) + energy  2 H2O (l)
H = ______________(+/-), S = ________________(+/-)
G = _______________ (+/-)and the reaction is _________________(spontaneous/not spontaneous).
NaOH(s)  Na+(aq)+ OH- (aq) + energy
H = ______________(+/-), S = ________________(+/-)
G = _______________ (+/-)and the reaction is _________________(spontaneous/not spontaneous).
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I. DBQ
Chemical based cold packs are often used to reduce swelling after an athletic
injury. These cold packs are disposable packs that you click or pop causing a
chemical reaction inside the pack. This chemical reaction is a controlled cooling,
usually just above the freezing point, lasting for approximately 15 minutes.
Chemical based cold packs can be taken and used anywhere. Cold packs work
through the reaction of gel or water with ammonium nitrate. When activated, the
ammonium nitrate draws all the heat from the water or gel.
1. Identify another reactant listed in Reference Table I that could be mixed with water for use in a
chemical cold pack.
2. If a cold pack was placed on an injury, describe the heat flow.
3. Is the cold pack an example of an endothermic or exothermic reaction?
4. Draw a potential energy diagram, describing this reaction.
5. What is the free energy of the reaction taking place in the cold pack?
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UNIT 9: Thermodynamics
1. Joule is a unit of heat measurement called q or H
ALL FORMULAS ARE FOUND ON TABLE T



H = mC T (M= mass of water, C = 4.18J/gC TABLE B, T= change in temp)
H = Mass of Water x Heat of Fusion - during melting phase change (TABLE B)
H = Mass of Water x Heat of Vaporization - during boiling phase change (TABLE B)
2. The heat of reaction (H) is the difference between the potential energy of products versus reactants
in a chemical reaction. H is also known as enthalpy.
H = Hproducts - Hreactants
ENDOTHERMIC REACTION:




Energy is absorbed (in)
products are less stable (higher in
energy) compared to reactants
H is (+)
Reactants + H  Products
EXOTHERMIC REACTION:




Energy is released
products are more stable(lower in
energy) than the reactants
H is (-)
Reactants  Products + H
3. Activation energy (AE) is the energy required to get to the activated complex, the point in the
reaction where all bonds are broken and new ones have not been made yet.
4. Heats of Reaction (H) for various reactions are found on TABLE I.
Remember :
- H represents exothermic reaction
+H represents endothermic reaction
5.
Entropy (S) is the amount of freedom/randomness/chaos of motion of particles. Solids have the
least entropy, gases have the most. Phase and molecular size determines if entropy is increasing or
decreasing.
6. Gibbs Free Energy (G) states if a chemical reaction will occur spontaneously.
G = H - T(S)
A reaction will be spontaneous if G is negative. This happens when the reaction is exothermic and
H is( - ), and entropy increases , when S is ( + ). A reaction will not be spontaneous if H is( + ),
and S is ( - ).