Thermochemistry pt 2

ΔH tracks energy flow as heat; ΔS measures disorder. Adding heat (ΔH↑) often increases molecular motion, raising disorder (ΔS↑)

ΔH and ΔS both measure temperature changes, but ΔS is faster.

They’re identical—both track energy released in reactions

Both paths release the same net energy. Like Hess's Law, the energy change depends only on start/end points, not the path.

Only the direct path follows Hess's Law because it's simpler

The indirect path releases more energy due to the extra lift

Hess's Law only applies to chemical reactions, not physical systems.

Water molecules break(dissociate) into H₂ and O₂ gas, absorbing 483.6 kJ/mol

Carbon bonds with hydrogen to form methane (CH₄)

Oxygen gas spontaneously decomposes into atoms

CO₂ forms immediately, releasing heat

It escapes as a gas product

It reacts with carbon to form CO₂, releasing 393.5 kJ/mol

It converts back into water

It dissolves into the solution

They double in quantity to form O₄

They remain as a final product

They cancel out because O₂ appears on both sides of the combined equation

They all become part of the CO₂ product

Spontaneous - happens without energy input

Isothermic - no energy change

Exothermic - net energy release

Endothermic - more energy absorbed than released

Add all formation enthalpies: ΔH°f(SO₂) + ΔH°f(O₂) + ΔH°f(SO₃)

[2×ΔH°f(SO₃)] − [2×ΔH°f(SO₂) + ΔH°f(O₂)]

Use only ΔH°f(SO₃) since it’s the main product

[2×ΔH°f(SO₂)] − [2×ΔH°f(SO₃)]

Breaking ionic bonds in solute AND intermolecular forces in solvent

Only breaking ionic bonds in the solute

Forming the solvation shell

Stirring the mixture

Separating solvent molecules

Breaking ionic bonds in the solute

Forming the solvation shell

Increasing the system's disorder

Only use the formation energy of the first product formed

Add together the formation energies of all chemicals in the reaction

Subtract the total formation energy of the starting materials from the total formation energy of the products

Average the formation energies of the starting materials and products