Enthalpy + Entropy

Enthalpy is what?

Heat AKA the change in energy if a system

At constant pressure: Change in enthalpy =

heat flow

Enthalpy is what type of function?

A state function

In a state function

path is independent

Enthalpy is positive (+) in what reactions?

Endothermic Reactions

Enthalpy is negative (-) in what reactions?

Exothermic Reactions

Endothermic Reactions:

Heat enters system (reactants + heat → products)

Exothermic Reactions:

Heat leaves system (reactants → products + heat)

Equation for Enthalpy:

H = U + PV

H:

U:

P:

V:

Enthalpy

Internal Energy

Pressure

Volume

Standard enthalpy change reaction occurs at:

25 C and 1 atm

Standard enthalpy of formation (DeltaH*f) is the change in enthalpy for the reaction that forms…

one mole of the compound from it’s elements in their standard states

Standard enthalpy of formation is 0 for:

Elements by itself including diatomic and when at standard state

If you flip a reaction should you change the sign of that ΔH?

Yes

If you multiply a reaction should you also multiply the ΔH?

Yes

Does enthalpy make a reaction spontaneous?

No

Combustion reaction involves what?

Its a fast, exothermic reaction involving a fuel and oxygen

Entropy measures what?

The randomness/disorder of a system

Entropy is a state function T/F?

True

Entropy is temperature dependent T/F?

True

How to find ΔSuniverse​

ΔSuniverse​=ΔSsystem​+ΔSsurroundings​

At Standard state, S is what?

1 bar for gases, liquids and solids

1 M for solutions

S _________ (slightly) as temperature rises

increases

S____________ as physical state becomes less ordered (as you go from solid to liquid to gas)

(solid < liquid<<gas)

increase

S often (but not always) ________ when substances are mixed. (An important exception is when gas is dissolved in a liquid)

increase

S__________as the number of molecules increases

increase

S usually___________ as molecules or atoms get bigger and more complicated

increase (size bigger = more room for chaos)

In a favorable/spontaneous reaction, the sign of ΔS is what?

Positive (+)

In a favorable/spontaneous reaction, the sign of ΔH is what?

Positive (+)

If you go from 3 moles of gas to 2 moles of gas, what does this mean?

less molecule = less chaos = Entropy (ΔS) decrease

Heat and entropy are what?

Proportional

Heat transferred to the surroundings raises entropy of the what?

surroundings

Temperature has small impact on entropy, but big impact on what?

spontaneous or not

If ΔG < 0 then ΔS is

> 0 spontaneous (exergonic)

If ΔG > 0 then ΔS is

< 0 Non-spontaneous (endergonic)

If ΔG = 0 then ΔS is

= 0 Equilibrium

What equation do you use to find free energy?

ΔG = ΔH - TΔSsys

ΔG is a ___________ function

state