Understanding Hess's Law in Chemistry

Hess's Law

Total enthalpy change is route-independent.

Enthalpy Change

Heat change at constant pressure during a reaction.

Hess Cycle

Diagram illustrating enthalpy changes in reactions.

Direct Route

Pathway from reactants to products directly.

Indirect Route

Pathway involving intermediate reactants or products.

ΔH_f

Standard enthalpy of formation per mole.

Calorimetry

Experimental measurement of heat changes.

Combustion Enthalpy

Heat change during the combustion of substances.

Standard Conditions

1 atm pressure and 298 K temperature.

ΔH_comb

Standard enthalpy change of combustion.

ΔH_atom

Enthalpy change for atomization of substances.

Average Bond Energy

Energy required to break one mole of bonds.

Balanced Equation

Chemical equation with equal atom counts.

Energy Cycle

Visual representation of enthalpy changes.

Reaction Pathway

Sequence of steps in a chemical reaction.

Mole

Quantity of substance containing 6.022 x 10^23 entities.

ΔH Calculation

Determining enthalpy change using Hess's Law.

Standard Enthalpy of Formation

Enthalpy change when one mole forms from elements.

C-H Bond Energy

Energy required to break a carbon-hydrogen bond.

Reactants

Substances consumed in a chemical reaction.

Products

Substances formed as a result of a reaction.

Thermochemical Equation

Chemical equation including enthalpy change.

Heat of Reaction

Heat absorbed or released during a reaction.

Stoichiometry

Calculation of reactants and products in reactions.

Standard Enthalpy Change

Enthalpy change under standard conditions.

ΔH Sign Convention

Positive for endothermic, negative for exothermic.

Thermodynamics

Study of energy changes in chemical reactions.