Hess's Law

Front

What is Hess's Law?

Back

Hess's Law states that the total enthalpy change for a reaction is the same, regardless of the number of steps the reaction takes.

Front

What happens to ΔH when a chemical reaction is reversed?

Back

The sign of ΔH is flipped.

Front

If a chemical equation is multiplied by a factor of 2, what happens to ΔH?

Back

ΔH is also multiplied by 2.

Front

What is the definition of Enthalpy?

Back

Enthalpy is a measure of the total heat content of a system, often represented as ΔH.

Front

What is Thermochemistry?

Back

Thermochemistry is the study of heat changes that accompany chemical reactions and phase changes.

Front

What does a positive ΔH indicate about a reaction?

Back

A positive ΔH indicates that the reaction is endothermic, meaning it absorbs heat.

Front

What does a negative ΔH indicate about a reaction?

Back

A negative ΔH indicates that the reaction is exothermic, meaning it releases heat.

Front

How does Hess's Law apply to multi-step reactions?

Back

Hess's Law allows us to calculate the total enthalpy change of a multi-step reaction by summing the ΔH values of each step.

Front

What is the significance of standard enthalpy of formation (ΔHf°)?

Back

The standard enthalpy of formation is the change in enthalpy when one mole of a compound is formed from its elements in their standard states.

Front

What is the formula for calculating ΔH using bond energies?

Back

ΔH = Σ(bond energies of reactants) - Σ(bond energies of products).