Thermodynamics

Thermal heat equilibrium

When hot and cold molecules collide, they create an average of the two to form a temperature (or new one)

Heat capacity

Amt of heat needed to raise temp of thing by 1 C “specific” = g “molar” = 1 mole

Q = mcΔT

Allows one to calculate heat transfer (amount of heat transferred or amount needed to make a specific change). Q = joules total m = mass C = specific heat of substance. and Delta T is the change in temp

Lower specific heat value…

Higher change in temperature

What is ΔH?

The change in heat (enthalpy).

What is enthalpy?

Heat at constant pressure

What is the delta H (change in heat) of a reverse reaction?

Flip the sign of the initial

What is constant during phase change?

Temperature (plateau)

Entropy (disorganization)

Measure of how spread out atoms and molecules become during chemical processes

Calculating enthalpy

Delta H reaction = products - reactants

How do we calculate entropy?

Delta S = final - initial

Gibbs Free Energy

G = spontaneity H = enthalpy T = Kelvin S = Entropy

High heat capacity means…

Less temperature change when exposed to heat

What comes out of the q=Mc^T?

Joules! (For Q)

How to find Q with Delta H?

Take the stoichiometry of the limiting reactant to the reaction (always 1) and cancel out to Kj

How to find qRxn in a calorimeter

Take the Q and make it negative (one gains, other loses)

How to find Delta H rxn?

The Qrxn divided by moles of the limiting reactant (these moles being divided by the stoich)

What does Delta H rxn tell us?

The energy per mole released in the reaction

What does reversing the equation do for Delta H?

Change its sign

For Delta H, what can we do when we change the stoichiometry?

Multiply Delta H by the new ratio. Double is 2x, ½ is 0.5x

How do we calculate the Delta H from several equations?

ADD, not multiply, their Delta Hs together

How to calculate enthalpy Delta H from bonds

Reactants enthalpy minus products enthalpy

Delta S, positive and negative

Positive = More entropy (less order)
Negative = Less entropy (more order)

What’s a good way to gauge if entropy increased?

More moles, more gases and liquids (more entropy)

How do we find Delta H from enthalpy?

Reactants minus products!

Delta H from Hf

Products minus reactants

Good way to remember products and reactants

Hf is products minus, everything else is reverse