How are Energy and Chemistry Related?
Unit 13: HW Packet
Name:___________________
_____ / 150 pts
Main Idea:
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Energy can change form and flow, but it is always conserved.
Thermochemical equations express the amount of heat released or absorbed
by chemical reactions.
The enthalpy change for a reaction can be calculated using Hess’s law.
Changes in enthalpy and entropy determine whether a process is
spontaneous.
New Skills:
 Calculate heat absorbed and heat released as temperature changes.
 Calculate calorimetry problems
 Determine enthalpy changes with phase changes
 Use Hess’s Law to determine enthalpy changes
 Calculate heat absorbed and heat released from reactions
 Determine entropy changes
 Calculate Free Energy
13.1 Energy and Heat - Energy can change form and flow, but it is always
conserved.
1. Define energy
a. (4pts) Define energy and include the two types of energy.
2. Distinguish between potential and kinetic energy.
a. (4pts) What is potential energy and chemical potential energy?
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b. (4pts) What is kinetic energy and how is it related to temperature?
c. (4pts)What does the Law of Conservation of Energy state and give an
example.
3. Calculate the amount of heat absorbed or released by a substance as its
temperature changes.
a. (4pts) Define heat and give two units that are typically used to measure
it.
b. (3pts) What is specific heat?
c. (4pts) Explain the relationship between sign and the direction of energy
flow.
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d. (6pts) How many joules of heat are lost by 3580 kg of granite as it cools
from 41.2 °C to -12.9°C? The specific heat of granite is 0.803 j/g°C.
e. (8pts) A swimming pool measuring 20.0m x 12.5 m is filled with water
to a depth of 3.75 m. If the initial temperature is 18.4°C, how much heat
must be added to the water to raise its temperature to 29.0°C? Assume
that the density of water is 1g/ml and water has a specific heat of 4.18
J/g°C.
f.
(8pts) When a 58.8 g piece of alloy at 106.1°C is placed in 135g of cold
water (19.8°C) in a calorimeter, the temperature of the water increases.
The alloy has a specific heat of .880 J/g°C and water has a specific heat
of 4.18 J/g°C. What is the final temperature of the water?
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13.2Thermochemical Equations- Thermochemical equations express the
amount of heat released or absorbed by chemical reactions.
1. Explain the meaning of enthalpy and enthalpy change in chemical reactions
and processes.
a. (3pts) What is thermochemistry?
b. (4pts) Define enthalpy and how is it represented?
c. (4pts) What is standard state and the specific numbers it represents? Is
it the same as standard temperature and pressure?
2. Describe how energy is lost or gained during changes of state.
a. (4pts) What is heat of vaporization? Is it endothermic or exothermic?
b. (4pts) What is heat of fusion? Is it endothermic or exothermic?
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3. Calculate the heat absorbed or released in a chemical reaction.
a. (6pts) Water is sprayed on a crop of vegetables. The water freezes that
night. How much heat is transferred for every liter of water that froze?
b. (6pts) What mass of propane (C3H8) must be burned in a barbecue grill
to release 4500 kJ of heat? The enthalpy of combustion of one mole of
propane is -2219 kJ/mol.
c. (8pts) Give the sign of energy flow and indicate whether the following is
endothermic and exothermic.
i. C2H5OH(s)  C2H5OH(l)
ii. H2O(g)  H2O(l)
iii. CH3OH(l)  CH3OH(g)
iv. NH3(l)  NH3(s)
13.3 Calculating Enthalpy Change1. Apply Hess’s law to calculate the enthalpy change for a reaction.
a. (6pts) Use Hess’s law and the changes of enthalpy for the following two
reactions to calculate ΔH for the reaction 2A + B2C3  2B + A2C3
i. 2A + 3/2 C2  A2C3 ΔH= -1874 kJ
ii. 2B + 3.2C2  B2C3 ΔH=-285 kJ
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2. Calculate the ΔHrxn using thermochemical equations.
a. (6pts) Solve for ΔH of C(s,diamond)  C(s, graphite) by using the following
information:
i. C(s, graphite) + O2(g)  CO2(g)
ΔH=-394 kJ
ii. C(s, diamond) + O2(g)  CO2(g)
ΔH= -396 kJ
3. Determine the enthalpy change for a reaction using standard enthalpies of
formation.
a. (6pts) Use standard enthalpies of formation from your reference sheet
to calculate ΔH for the following reaction:
i. P4O6(s) + 2O2(g)  P4O10(s)
13.4 Reaction Spontaneity- Changes in enthalpy and entropy determine
whether a process is spontaneous.
1. Define Entropy.
a. (3pts) Define entropy.
b. (4pts) When a solid sublimes, does entropy increase or decrease and
why?
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c. (3pts) What is the second law of thermodynamics?
d. (8pts)
i.
ii.
iii.
iv.
Give the sign of entropy change for the following processes:
C2H5OH(s)  C2H5OH(l)
H2O(g)  H2O(l)
CH3OH(l)  CH3OH(g)
NH3(l)  NH3(s)
2. Differentiate between spontaneous and nonspontaneous processes.
a. (6pts) Define spontaneous and what two things must be considered to
determine if a reaction is spontaneous?
3. Explain how changes in entropy and free energy determine the spontaneity
of chemical reactions and other processes
a. (8pts) Calculate the ΔG for the following systems at 29°C:
i. ΔH= 145 K, ΔS = 195 kJ
ii. ΔH= -232kJ, ΔS = 138 kJ
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13.5 Accumulating Content and Skills– Chemistry content is continuous and
builds on prior knowledge and skills. This section will combine this unit with previous
units.
1. Apply knowledge and skills from previous units to content learned in this
unit.
a. (12pts) Predict the typical enthalpy and entropy changes for the four
main types of reactions:
 Synthesis
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Decomposition
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Combustion
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Replacement
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