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Apologia Chemistry Module 13

Terms in this set (29)

Enthalpy (H)
The energy stored in an object
Change in Enthalpy (∆H)
The energy change that accompanies a chemical reaction

(often referred to as just enthalpy)

kJ/mole or kcal/mole
1 calorie
4.184 Joules
∆H is _______ for endothermic reactions
positive
∆H is _______ for exothermic reactions
negative
When a reaction is exothermic, energy is thought of as a _______.
product
When a reaction is endothermic, energy is thought of as a _______.
reactant
Bond energy
A measure of the strength of a chemical bond
∆H =
energy required to BREAK bonds - energy RELEASED when bonds formed
State function
Any quantity that depends solely on the final destination, not on the way you get to that destination
Hess's Law
Enthalpy is a state function and is therefore independent of path

(the amount of energy in a substance is independent of how it is made)
Enthalpy of Formation (∆H(f))
The ∆H of a formation reaction
Standard conditions
25°C and 1.00 atm
Standard enthalpy of formation (∆H(f)°)
∆H(f) measured at 25°C and 1.00 atm
∆H°
∑∆H(f)°(products) - ∑∆H(f)°(reactants)
The ∆H(f)° of an element in its elemental form is _______
0
Activation energy
The energy necessary to start a chemical reaction
Entropy (S)
A measure of the disorder that exists in any system

Joules/mole*K OR kcals/mole*K OR kJ/mole*K
Second Law of Thermodynamics
The entropy of the universe must always either in crease or remain the same. It can never decrease.
The _______ state has the least amount of entropy associated with it.
solid
The entropy of a system _______ with increasing temperature.
increases
The entropy of a system ______ as the matter it contains increases.
increases
∆S° =
∑∆S°(products) - ∑∆S°(reactants)
Gibbs Free Energy (∆G)
∆H - T∆S

where T = temperature of surroundings (in Kelvin)
When ∆G < 0, the reaction
is spontaneous
When ∆G > 0, the reaction
cannot proceed
An exothermic reaction that increases energy ...
is always spontaneous
An endothermic reaction that decreases entropy ...
will never occur
The ∆G°(f) of any element in its elemental form is _______
0
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