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CHM 1045 - Chapter 6
Terms in this set (44)
The capacity to do work.
Directed energy change resulting from a process.
Force X Distance
Not a state function
𝑤 = -PΔV
Energy produced by a moving object.
Energy that comes form the sun and is Earth's primary energy source.
Energy associated with the random motion of atoms and molecules.
Can be calculated from temperature measurements.
A cup of hot coffee has a greater temperature than a bathtub filled with water, but the bathtub water has a greater thermal energy because is has a much larger mass and a much larger volume, equating to more water molecules and more molecular motion.
Stored within the structural units of chemical substances.
When substances participate in chemical reactions, chemical energy is released, stored, or converted to other forms of energy.
Can be considered a form of Potential Energy because it is associated with the relative positions and arrangements of atoms within a given substance.
Energy available by virtue of an object's position.
Law of Conservation of Energy
The total quantity of energy in the universe is assumed constant.
When one form of energy disappears, some other form of energy (of equal magnitude) must appear.
Transfer of thermal energy between two bodies that are at different temperatures.
Not a state function
Study of heat change in chemical reactions.
Specific part of the universe that is of interest to us.
Rest of the universe outside of the system.
Can exchange mass and energy usually in the form of heat with its surroundings.
Allows the transfer of energy, but not mass.
Does not allow the transfer of mass or energy.
"Exo" = "Outside"
Process that gives off heat.
Transfers heat to the surroundings.
"Endo" = "Within"
Energy has to be supplied to the system by the surroundings.
Interconversion of heat and other kinds of energy.
We study the changes of the state of a system.
State of a System
Values of all relevant macroscopic properties; such as composition, energy, temperature, pressure, and volume.
Properties determined by the state of the system regardless of how that condition was achieved.
Energy, temperature, pressure, and volume.
When the state of a system changes, the magnitude of change in any state function depends only on the initial and final states of the system, not on how the change was accomplished.
Final - Initial
First Law of Thermodynamics
Energy can be converted from one form to another, but cannot be created nor destroyed.
Energy gained in one place must have been lost somewhere else.
ΔU system + ΔU surrounding = 0
ΔU system = -ΔU surrounding
ΔU = 𝑞 + 𝑤
The change in internal energy, ΔU, of a system is the sum of the heat exchange 𝑞 between a system and its surroundings, and the work done 𝑤 on (or by) the system.
work done on the system by the surroundings
, and is
work done by the system on the surroundings.
ΔV > 0
-PΔV is a negative quantity
If a reaction under constant pressure results in a net increase in the number of moles of a gas - the system does work on the surroundings.
ΔV < 0
-PΔv is a positive quantity
If a reaction under constant pressure results in a net decrease in the number of moles of a gas - work is done on the system by the surroundings.
L ∙ atm to Joule conversion
101.3 J / 1 L ∙ atm
Watt to Joule
E = P(watts) x T(time in sec)
J = Watt/second
H = U + PV
U = Internal energy of the system
P = Pressure
V = Volume
U,P,V are state functions so the changes in them depend only on the initial and final states. Because of this, ΔH is also a state function.
Enthalpy of a Reaction at Constant Volume
Heat change is equal to the change in energy
qᵥ = ΔU
Enthalpy of a Reaction at Constant Pressure
Heat change is equal to ΔH
qᴾ = ΔH
Enthalpy of Reaction
Difference between the enthalpies of the products and the enthalpies of the reactants.
Endothermic Process (Heat absorbed by system from surroundings)
--> ΔH is positive or >0
Exothermic process (Heat released by the system to the surroundings)
--> ΔH is negative or <0
Show the enthalpy changes as well as the mass relationships.
Reactions that don't involve a change in the number of moles of a gas from reactants to products.
ΔU = ΔH
H₂(g) +F₂(g) --> 2HF (g)
Measurement of heat changes
Specific Heat (s)
Amount of heat required to raise the temperature of 1g of the substance by 1°C.
J/g x °C
- physical property of a system that does not depend on system size or amount of material in the system. Ex - hardness of a diamond
Heat Capacity (C)
Amount of heat required to raise the temperature of a given quantity of the substance by 1°C.
- proportional to the amount of material in a system. Ex - Mass and Volume
Relationship Between Specific Heat and Heat Capacity
m = mass of the substance in grams
Equations for Calculating Heat Change
q = msΔt
q = CΔt
q is positive for endothermic processes and is negative for exothermic processes.
Standard Enthalpy of Formation
The standard enthalpy of formation for any substance in it's most stable form is zero.
The heat change that results when 1 mole of the compound is formed from it's elements at a pressure of 1 atm.
Substances are said to be in the
at 1 atm
° Stands for standard-state conditions
𝑓 stands for formation
Standard Enthalpy of Reaction
Enthalpy of a reaction carried out at 1 atm.
∑𝑛ΔH°𝑓(products) - ∑𝑚ΔH°𝑓(reactants)
𝑚 and 𝑛 denote the stoichiometric coefficients of the reactants and products respectively.
When reactants are converted to products, the change in enthalpy is the same whether the reaction takes place in one step or in a series of steps.
Heat of Solution
Enthalpy of Solution
Heat generated or absorbed when a certain amount of solute dissolves in a certain amount of solvent.
ΔHˢᵒˡⁿ = U +ΔHʰʸᵈʳ
Lattice Energy (U)
Energy required to completely separate 1 mole of a solid ionic compound into gaseous ions.
Lattice Energy is a
Heat of Hydration
Heat of hydration is a negative quantity for cations and anions.
Heat of Dilution
Heat change associated with the dilution process.
If a solution process is
and the solution is diluted,
heat will be
by the same solution from the surroundings.
If a solution process is
and the solution is diluted.
heat will be
by the same solution form the surroundings.
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