Unit 5 Review: Energy
Please answer all the following questions as completely as possible. Include all work and all units for the
following problems and don’t forget to have your final answer go to the hundreds place. Remember all
material in Unit 5 is fair game so make sure to study this plus your notes plus use those other worksheets on
Canvas as additional practice!
1. Write nuclear equations for the following:
a. Iron-59 is undergoing beta decay
b. Technetium-99 is undergoing 2 alpha, 1 beta and 1 gamma decay
2. In the above nuclear reactions, what is happening in the nucleus of the isotopes after radiation is
emitted?
3. Sodium-24 has a half-life of 15 hours. How much sodium-24 will remain in an 18.0 g sample after 60
hours?
4. Polonium-214 has a relatively short half-life of 164 seconds. If we start with 8 grams of this material,
what would be left after 1,148 second?
5. Explain the differences between fission and fusion in terms of definition, energy and radiation.
6. Determine if the following example are endothermic or exothermic:
a. The bag gets colder when Ammonium chloride dissolves
b. Block of ice melts in the sun
c. A balloon shrinks when placed over ice
d. Ethanol vaporizes when heated by a person’s hands
7. How many Joules of heat energy would be required to raise the temperature of 16.0g of lead from
25˚C to its melting point of 327˚C for a length of time long enough to completely melt the lead. The
specific heat capacity of lead is 0.159 J/g*K.
8. Silver and sodium have a specific heat of 0.233 J/g*˚C and 1.20 J/g*˚C respectively.
a. 40 grams of each at 20˚C are placed on a hot stove for the same amount of time. Which metal
will have a higher temperature when they are removed from the stove?
b. 20 grams of each at a temperature of 15˚C are heated until they reach 50˚C. Which metal
requires more energy?
9. When 221 grams of water at a temperature of 25˚C are mixed with an unknown mass of water at a
temperature of 57˚C, the final temperature of the resulting mixture is 33.1˚C. What was the mass of
the second sample of water?
10. When a piece of aluminum weighing 35.7g and a temperature of 81.9˚C is placed in a calorimeter
containing 75g of water at 24.9˚C, the temperature increases to 28.3˚C. If the specific heat of the
aluminum is 0.902J/g*˚C, what is the calorimeter constant?
11. The reaction for the fermentation of glucose is …
C6H12O6 (aq)  2CO2(g) + 2C2H5OH(aq) ΔHrxn = -67kJ
Is this reaction endothermic or exothermic?
12.
a. Label the reactants, products, Ea, and ∆H
b. What is the activation energy value for the forward reaction?
c. What is the ∆H for the forward reaction?
d. Is this forward reaction endothermic or exothermic?
Multiple Choice Questions: Choose the one correct answer to each question
13. When balancing the following nuclear reaction, what is the identity of element X?
238 U → 234 X + 4 He
92
90
2
a. Pu
b. Np
c. Th
d. Pa
14. This reaction 21084Po →
a. Alpha decay
b. Beta decay
c. Gamma decay
d. Positron decay
206
82Pb
+ _____ is an example of:
15. What happens to the mass number and the atomic number of an element when it undergoes beta
decay?
a. Neither the mass number nor the atomic number change
b. The mass number decreases by 4 and the atomic number decreases by 2
c. The mass number does not change and the atomic number increases by 1
d. The mass number does not change and the atomic number decreases by 2
16. Water condensing from a gas to a liquid is:
a. Endothermic
b. Like rain?
c. Exothermic
d. What is water?
17. In a chemical reaction, if more energy is required to make the chemical bonds than to break them
apart, the reaction is endothermic so we see a:
a. No change in temperature
b. Huh?
c. Decrease in temperature
d. Increase in temperature