Module 13: Thermodynamics

When a reaction is exothermic, energy will be thought of as ______________.
When a reaction is exothermic, energy will be thought of as a product in the reaction. (417)
When a reaction is exothermic, energy will be considered _______________.
When a reaction is exothermic, energy will be considered a reactant. (417)
The energy stored in a substance is called the ___________ of that substance.
enthalpy
(symbol: H)
Change in Enthalpy (?H)
The energy change that accompanies a chemical reaction. (419)
1 calorie = ________ Joules
1 calorie = 4.184 Joules (419)

ΔH is [positive/negative] for

endothermic reactions.

positive (419)

ΔH is [positive/negative] for

exothermic reactions.

negative (419)
Bond energy

The energy required

to break a bond.

(424)

Hess’s Law

Enthalpy is a state function

and is therefore

independent of path.

(429)

State function

Any quantity that depends solely

on the final destination,

not on

the way you get to that destination.

(429)

Enthalpy of formation

(;Hf)

The ;H of

a formation reaction.

(430)

;

What are standard enthalpies of formation?

Standard conditions under which most chemistry is done:

  • room temperature (25; Celsius)
  • normal atmospheric pressure (1.00 atm)

(430)

In the symbol ;Hf0

what does the “0” tell you?

That the enthalpy of formation

was measured

under standard conditons.

(430)

;

What is the

standard enthalpy of formation

of an element in its elemental form?

zero

(431)

Energy diagram

Diagram that shows:

  • the energy of the reactants
  • intermediate state
  • products; in a chemical reaction.

(436)

Reaction coordinate

Coordinate which tells

how close the reaction is to completion.

(436)

Intermediate state

A complex formed

in the process of a chemical reaction

when the reactants and products

are interacting.

(436)

Activated complex

Another name

for the intermediate state

of a chemical reaction.

(436)

Activation energy

The energy necessary

to start a chemical reaction.

(437)

Entropy

A measure of

the disorder that exists in any system.

(437)

Second Law of Thermodynamics

The entropy of the universe must always either increase or remain the same.;

It can never decrease.

(440)

What are

the relative entropy phases of matter?

(solid, liquid, gas)

;

  • solid (least amount of entropy)
  • liquid (greater amount of entropy)
  • gas (highest amount of entropy)

(441)

With rising temperature,

the entropy of a system [increases/decreases].

increases

(441)

As the matter it contains increases,

the entropy of a system [increases/decreases.

increases

(441)

Second Law of Thermodynamics

(mathematical equation)

;Suniverse ; 0

;

(442)

All substances, even elements,

have ___________________.

an absolute entropy.

(443)

Gibbs Free Energy (;G)formula

;G = ;H – T;;S

;

(446)

Standard enthalpy of formation

The ;H of a formation reaction at

T = 298 K and P = 1.00 atm

(430)

A reaction that is

consistent with the Second Law of Thermodynamics is said to be ____________.

spontaneous

(446)

A reaction is called;not spontaneous

when it is not consistent with the Second Law of Thermodynamics because ____________.

the reaction cannot occur.

(446)

When ;G ; 0,

then the reaction is

consistent with the Second Law,

and is therefore _____________.

spontaneous.

(447)

If ;G ; 0,

then the reaction cannot proceed,

because it violates __________________.

the Second Law of Thermodynamics.

(447)

x

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