3 Methods

[Guadalupe T 1E]

I know we use three methods, but what exactly are they used for? What are we trying to find?

[Clarisse Wikstrom 1H]

Enthalpy of the total reaction.

[Ammar Amjad 1L]

You are calculating the ∆H (change in enthalpy). There are three methods to get this.
Method 1: Hess's Law
Enthalpy changes are additive. Enthalpy change at each step of a multi-step reaction can be added to give the total enthalpy change.
Method 2: Bond Enthalpies
Add up all new bonds formed (energy released), and all bonds broken (energy required) to get ∆H.
Method 3: Standard Reaction Enthalpies
If bond enthalpies are not given, one can calculate the standard reaction enthalpies by calculating the standard enthalpy of formation of all products and subtracting the standard enthalpy of formation of all reactants. (Use of tables of standard enthalpy of formation to calculate.)