Chapter 17 review
Important Vocabulary
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Thermochemistry- Studies of energy changes that occur during chemical
reactions and change state
Chemical potential energy- The energy stored in the chemical bonds of a
substance
Heat- Represented by q, is energy that transfers from one object to another
because of temperature difference between the objects
System- Part of the universe on which you focus your attention
Surroundings- Everything else in the universe
Law of conservation of energy- in any chemical or physical process,
energy is neither created or destroyed
Endothermic process- Heat is absorbed from its surroundings
Exothermic process- One that releases heat to its surroundings
Specific heat- the amount of heat it takes to raise the temperature of 1 g of
the substance 1 degree
Heat capacity- the amount of heat needed to increase the temperature of
an object exactly one degree celcius
Calorimetry- the measurement of the heat flow into or out of a system for
chemical and physical processes
Calorimeter- the insulated device used to measure the absorption or
release of heat in chemical or physical processes
Enthalpy- accounts for the heat flow of the system at constant pressure
Thermochemical equations- A chemical equation that includes the
enthalpy change
Heat of reactions- the enthalpy change for the chemical equation exactly
as it is written
Heat of combustion- heat of reaction for the complete burning of one mole
of a substance
Molar heat of fusion- The heat absorbed by one mole of a solid substance
as it melts to a liquid at a constant temperature
Molar heat of solidification- Heat lost when one mole of liquid substance
solidifies at a constant temperature
Molar heat of vaporization- The amount of heat required to vaporize one
mole of given liquid at a constant temperature
Molar heat of condensation- amount of heat released when one mole of a
vapor condenses at its boiling point
Molar heat of solution- The enthalpy change caused by the dissolution of
one mole of a substance
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Hess’ law of heat summation- If you add two or more thermochemical
equations to give a final equation, then you can also add the heats of
reaction to give you the final heat of reaction
Standard heat of formation- the change in enthalpy that accompanies the
formation of one mole of a compound from its elements with all
substances in their standard state
Important information
Specific heat (C) is measured in cal/g per degree celcius
Important Equations
1. ! = !"∆!
m=mass (g)
C= Specific heat
∆ = change in heat (!! − !! ) = !
!
2. ∆! = !"#
Enthalpy
(!)! (!)!
3. !× (!)! (!)!
Rate of reaction
(!)! (!)!
4. K=(!)! (!)! Equilibrium
Important Notes
1. Gibbs law
a. When the change in energy is negative, the reaction is favored
b. When the change in energy is positive, the reaction is unflavored
c. When there is no change in energy, the reaction is at equilibrium
2. In an equilibrium equation, whenever there is only one reactant in the
denominator, you multiply that by K to give you !!"
a. !!" = 1.8×10!!
Review Questions
Multiple choice
1. What happens to the water in a calorimeter when an exothermic reaction
occurs in it?
A. It absorbs heat, and a drop in temperature is observed.
B. It absorbs heat, and a rise in temperature is observed.
C. It releases heat, and a drop in temperature is observed.
D. It releases heat, and a rise in temperature is observed.
2. How many joules are in 148 calories? (1 cal = 4.18 J)
a.
6.61 J
b.
148 J
c.
35.4 J
d.
619 J
3. Which of the following is a valid unit for specific heat?
a. cal/g°C
b. cal
c. cal/g
d. °C
4. A process that absorbs heat is a(n) ____.
A .endothermic process
B. exothermic process
C. polythermic proces
D. ectothermic process
Short answer
1. Explain the difference between system and surrounding
2. Determine the equilibrium when PbCr!! → !" + !"!!
3. How many kJ are required to heat 45.0 g of H2O at 25.0 °C? C=4.184
Answers
1.
2.
3.
4.
b
c
a
a
5. A system is a specific point and the surrounding is the entire universe
6. 1.3×10!!
7. 14.121 Kj