17.4 chemistry

What are the 2 indirect ways to find ΔHΔH when calorimetry isn't possible?

1. Hess's Law of Heat Summation

2. Standard Heats of Formation (ΔHf∘)

what is Hess's Law of Heat Summation?

If a reaction is carried out in a series of steps, the overall enthalpy change equals the sum of the enthalpy changes for the individual steps

2 Rules for Manipulating Equations in Hess's Law

1. Reverse the equation →flip the sign of ΔH (+ becomes −, or vice versa).

2. Cancel out identical species appearing on both the reactant and product sides in intermediate steps

what is Standard Heat of Formation (ΔHf∘​)

The heat absorbed or released when 1 mole of a compound is made from its pure elements under standard conditions (25∘C, 101.3 kPa).

what is Zero Rule for Free Elements?

Any pure, uncombined element in its normal state at room temperature has a ΔHf∘=0 kJ/mol