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The vaporization of Br2 from liquid to gas state requires 7.4 k/cal mol. A. What is the sign of the change in heat for this process?
Positive
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The vaporization of br2 from liquid to gas state requires 7.4 k/cal /mol. B. how many k/cal are needed to vaporize 5.8 mol of br2?
43 k/cal
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The vaporization of Br2 from liquid to gas state requires 7.4 k/cal /mol. C. How many k/cal are needed to evaporate 82 g of Br2?
3.8 k/cal
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7.2: Converting liquid water to solid ice releases 1.44 kcal/mol. A. What is the sign of change in heat for this process?
Negative
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7.2 B: how many k/cal are released by freezing 2.5 mol of h2o?
3.6 k/cal
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7.2 C: How many k/cal are released by freezing 32g of h2o?
2.56 k/cal
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7.2 D: How many k/cal are absorbed in melting 1mol of ice?
1.44 k/cal
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7.3 During the combustion of 5g of octane (C8H18), 239.5 k/cal is released: 2 C8H18 + 25 O2 = 16 CO2 + 18 H2O.
A. What is the sign of change of heat for this reaction?
Negative
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7.3 B. How much energy is released by the combustion of 1mol of octane?
5460.6 k/cal
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7.3 C. How many grams and how many moles of octane must be burned to release 450 k/cal?
9.39g; 0.082mol
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7.3 D. How many k/cal are released by the combustion of 17g of octane?
814.3 k/cal
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7.4 Which of the following processes results in an increase in entropy of the system? A. A drop of ink spreading out when it is placed in water.
Increase
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7.4 B. Steam condensing into drops on windows.
Decrease
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7.4 C. Constructing a building from loose bricks.
Decrease
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7.5 Entropy increase or decrease.
A. Assembling a jigsaw puzzle
Decrease
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7.5 B
I2 (s) + 3 F2 (g) = 2 IF3 (g)
Decrease
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7.5 C
A precipitate forming when two solutions are mixed
Decrease
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7.5 D
C6H12O6 (aq) + 6 O2 (g) = 6 CO2 (g) + 6 H2O (g)
Increase
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7.5 E
CaCO3 (s) = CaO (s) + CO2 (g)
Increase
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Pb(NO3)2 (aq) + 2 NaCl (aq) = PbCl2 (s) + 2 NaNO3 (aq)
Decrease
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What is meant by spontaneous process?
One that happened under the given set I conditions. For example the melting point of ice is spontaneous at temperature above 0 Celsius
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How is the sign of the free energy change (^G) related to the spontaneity of a process?
If the free energy change is negative the rxn is spontaneous; if the free energy change is positive the rxn is non-spontaneous
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Name three factors that affect the spontaneity of a process
Enthalpy change (^H), Entropy change (^S), and temperature
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What is the difference between an exothermic and an exergonic reaction?
- Exothermic reaction is one that has a negative ^H and releases heat. This type of reaction may or may not be spontaneous.
- Exergonic reaction is one that has a negative ^G and releases free energy and is spontaneous
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What is the difference between an Endothermic and Endergonic reaction?
- Endothermic reaction is one that has a positive ^H and absorbs heat. May or may not be spontaneous.
- Endergonic reaction is one thy has a positive ^G and absorbs free energy and is non-spontaneous
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7.11 For this reaction:
NaCl (s) -----> Na2+ (aq) + Cl- (aq) ^H = +1.00 k/cal
A. Is this process endothermic or exothermic?
Ednothermic
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7.11
B. Does entropy increase or decrease in this process?
Increase
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7.11
C. Table salt (NaCl) readily dissolves in water. Explain
Spontaneous because the increase in entropy "outweighs" the fact that it is endothermic, causing the free energy change for the process to be negative.
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7.12
The reaction of gaseous H2 and liquid Br2 to give the gaseous HBr has ^H= -17.4 kcal/mol and ^S=27.2 cal/(mol K).
A. Does entropy increase or decrease in this process?
Increase
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7.12
B. Is this process spontaneous at all temperatures?
Since ^H and ^S both favor spontaneity, this reaction will be spontaneous at all temperatures.
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7.12
C. What is the value of ^G for the reaction at 300 K?
-25.6 kcal/mol
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7.13
What is the activation energy of a reaction?
The energy that must be supplied to make th ereaction happen. It can be thought of as the "energy barrier" for the reaction. If the activation enery is not supplied, the reaction will not happen.
The rate of the reaction will depend on the activation energy. Reactions with large activation energies will generally be slower than reactions with smaller activation energies.
On an energy diagram, the activation energy is the energy difference bewteen the energy of the reactants and the highest point on the energy diagram.
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7.14
Draw energy diagrams for reaction that meet the following descriptions:
A. A fast exergonic reaction that has a small free energy change.
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7.14
B. A slow endergonic reaction that has a large free-energy change.
 - ^G < 0 ^G > 0
- Spontaneous Non-spontaneous
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7.15
Give 2 reasons why increasing temperature increases the rate of reaction.
- Higher temperatures increase the motion of reactants and therefore the frequency of collisions.
- Higher temperature also increase the energy of reactants.
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7.16
What is a catalyst and what effect does it have on the activation energy of a reaction?
A catalyst speeds up a reaction by lowering the activation energy of the reaction.
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7.17
What is meant by the term "chemical equillibrium"?
Must amounts of reactants and products be equal at equillibrium?
- When a system is in chemical equillibrium, the rate of the forward reaction is the same as the rate of the reverse reaction.
- At equillibrium it is not necessarily the case tha the concentration of the reactant is the same as the concentration of the products.
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7.18
Write the equillibrium equations for the following reactions:
A. 2 CO (g) + O2 (g) <--> 2 CO2 (g)
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7.18
B. 3 O2 (g) <---> 2 O3 (g)
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7.19
For the reaction N2O4 (g) <---> 2 NO2 (g), the equillibrium concentraions at 25 deg C are [NO2]=0.0325 mol/L and [N2O4]=0.147 mol/L.
What is the value of K at 25 deg C?
0.0072
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7.20
Oxygen can be converted into ozone by the action of lighting or electric sparks:
3 O2 (g) <---> 2 O3 (g)
For this reaction, ^H= +68 kcal/mol and K= 2.68 x 10^-29 at 25 deg C.
A. Is the reaction exothermic or endothermic?
Endothermic
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7.20
B. Are the reactants or the products favored at equillibrium?
Reactants
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7.20
C. Explain the effect on the equillibrium of:
1) increasing pressure by decreasing volume
2) increasing the concentration of O2 (g)
3) increasing the concentration of O3 (g)
4) adding a catalyst
5) increasing the temperature
- 1) shift right
- 2) shift right
- 3) shift left
- 4) no shift
- 5) shift right
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