Home > Chemistry > Chemistry 1A Part Deux: Lecture 23 Notes

Chemistry 1A Part Deux: Lecture 23 Notes

Overview

Today is a 51 minute lecture on the calculation of heat.

Details

Heats of reaction can be measured by calorimetry or calculated by using tabulated values of heats of formation.

Which reaction releases the most heat?

A C(s) + O2(g) = CO2(g)

B C(g) + 2O(g) = CO2(g)

C They are the same

dH is zero when reactants, products far below.  The formation of O2 and C gas has already released some heat.  They are already in their steady state.

Interesting chart at 20:27 in.  As time has gone one, we use more and more energetic reactions.

4 Au + 3 O2 = 2Au2O3   dH = +131 Gold -6000 BCE

Adding heat is not enough to extract metal from metal oxides!

The standard enthalpy of formation of a compound is the enthalpy change for the reaction that produces one mole od the compound from its elements in their most stable, standard states.

Hess’ Law

If two or more chemical equations are added to give another chemical equation, the corresponding enthalpies of reaction can be added to obtain the desired enthalpy of reaction.

Enthapies are state functions.  It does not matter what path is taken.

d H reaction = Energy required to break bonds + energy released to make bonds.

Review

PV = nRT

(P + n2/a2) (V – nb) = nRT

IGL: point source, random motion, elastic collisions, high temperature, low pressure

K =products/reactants

Bronsted acids donate protons, bronsted bases accept protons

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