Use the following information to answer Questions 1 and 2.
When solid potassium is placed in a beaker of water at room temperature,
an immediate, violent reaction occurs:
2K(s) + 2H_2O(l) --> 2KOH(aq) + H_2(g) + ENERGY 1. Sketch and label an energy pathway diagram for this reaction.
Your diagram should include:
• labelling of the X and Y axes
• general shape of the energy pathway
• labeling of the reactant plateau, the product plateau, the
activation energy (Ea) and the change in enthalpy (ΔrH)
No specific numerical values are required. 2. Refer to the diagram you drew in Question 1. When solid potassium is
placed in a beaker of water at room temperature, what should happen to
the temperature of the water? Use the following information to answer Questions 3-6. Sucrose, commonly known as table sugar, will be hydrolyzed to fructose and
glucose in the presence of the enzyme sucrase. The reaction equation for
this hydrolysis is
The energy changes for this reaction are diagramed below.
The blue line represents the reaction progress with sucrase and the red line
represents the reaction progress without sucrase.
3. The enzyme sucrase will ____.
A.increase the reaction rate of the hydrolysis of sucrose.
B.provide an alternate pathway, with higher Ea, for the hydrolysis of sucrose
C.lower the value of ΔH.
D.change the reaction from exothermic to endothermic
4.Because it lowers the activation energy, the enzyme sucrase is classified
as a _______.
Answer 5. Describe how adding a catalyst to a reaction system affects the enthalpy
change for the overall reaction.
Answer 6. Identify which energy value is indicated by each of the numbers in the
above energy pathway diagram.
Answer
Numbe Energy value r Change in enthalpy for both forward and reverse reaction
Uncatalyzed activation energy for the forward reaction
Uncatalyzed activation energy for the reverse reaction
catalyzed activation energy for the reverse reaction
catalyzed activation energy for the forward reaction Use the following information to answer Questions 7-11.
Dinitrogen pentaoxide, N2O5(g), is a strong oxidizer that forms explosive
mixtures with organic compounds and ammonium salts. At standard state,
dinitrogen pentaoxide decomposes into NO HYPERLINK
"http://en.wikipedia.org/wiki/Nitrogen_dioxide"2 and O HYPERLINK "http://en.wikipedia.org/wiki/Oxygen"2 according
to the following equation.
2N_O_5(g) + 219 kJ --> 4 NO_2(g) + O_2(g) 7. The above reaction is __i__ and the standard enthalpy of reaction is
__ii__.
The statement above is completed by the information in row_____.
Row
A.
B.
C.
D. i
endothermic
endothermic
exothermic
exothermic ii
Hoo= + 219 kJ
rH = - 219 kJ
o
H
= + 219 kJ
r
o
H
= - 219 kJ
r
r 8. Calculate the standard molar enthalpy of reaction for dinitrogen
pentaoxide.
Answer 9.Sketch and label a chemical potential energy diagram for the above
process. Indicate the enthalpy change using r as a subscript.
Answer 10. When 10.0 mol of nitrogen dioxide is produced in the above reaction,
the enthalpy change is ____kJ
Answer 11.Is energy absorbed or released in the above reaction?
Answer Use the following information to answer Question 12.
Cyclopropane is an anaesthetic when inhaled. When the gas is mixed with
oxygen there is a significant risk of explosion. Consequently, the use of
cyclopropane as an anaesthetic was phased out as safer alternates were
developed. Cyclopropane combusts according to the following reaction
2C_3H_6(g) + 9 O_2(g) --> 6 CO_2(g) + 6 H_2O(g) Δ_cH°= .3918.4 kJ
12. Calculate the standard molar enthalpy of combustion for
cyclopropane. Show all work for full marks.
Answer Use the following information to answer Questions 13-16.
Galvanizing is the process of coating an object with zinc. When exposed to
oxygen, zinc forms an oxide coating that protects the metal from further
corrosion. At standard state, this reaction is represented by the following
equation.
Zn(s) + 1/2 O_2(g) --> ZnO(s) + 350.5kJ
13.Sketch and label a chemical potential energy diagram for the
above process. Indicate the standard enthalpy of reaction using r as a
subscript.
Answer 14. The formation of zinc oxide is classified as an
__i_(endothermic/exothermic) reaction, and the reactants have __ii__
(less/more) potential energy than the products.
Answer
i
ii
15. When the above reaction occurs, it is expected that the temperature of
the surroundings will __i__ (decrease/increase). This change in
temperature would indicate that the surroundings are undergoing a change
in __ii__ (kinetic/potential) energy.
Answer
i
ii
16. Calculate the standard enthalpy of reaction when 25.0 g of zinc
oxide is produced. Show all work for full marks.
Answer Use the following information to answer Questions 17 and 18.
Welding utilizes a variety of fuels. Two such fuels identified for
comparison are acetylene (ethyne C2H2(g)) and propylene
(propene C3H6(g)).
Fuel
acetylene Molar enthalpy of combustion
(kJ/mol)
-1 300.8 propylene -2 058.1 17.Calculate and compare the values of the enthalpy of combustion in kJ/g
for each fuel.
Answer 18. Describe two other factors that can be used to evaluate the fuel.
Answer

 

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