The Energy of Physical, Chemical Processes
Thermodynamics

The study of energy and energy transfer
Thermochemistry

The study of energy involved in chemical reactions
Law of conservation of energy

Total energy of the universe is constant.
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Energy is neither created or destroyed
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Energy can be transferred from one substance to another
Demo exo and endo
System

Part of the universe that is being studied and observed

In chemistry this is the reactants and products
Surroundings

Everything else in the universe surrounding the system
Heat and Temperature
Heat, Q

Transfer of kinetic energy, expressed in units of energy (J)Joules

Heat is transferred from warmer objects to cooler objects.
Temperature, T

Measure of average kinetic energy of the particles that make up a substance or system.

Measured in Celsius (C) or Kelvin (K)

Temp in Kelvin = C + 273.15

Enthalpy (H)

Total internal energy of a substance



Chemists study enthalpy change,
Enthalpy change is equivalent to its heat change at constant pressure
Enthalpy changes result from bonds being broken and formed.
Breaking bonds requires energy, Creating bonds release energy.
Endothermic Reaction

A reactions that results in an absorption of energy
Exothermic Reactions

A reaction that results in a release of energy
Representing Exothermic reactions
Exothermic reactions can be shown in 3 ways
1.
A balanced chemical equation that indicates the amount of heat that is absorbed or released by the reaction it represents

2.
You can also put enthalpy as a separate expression beside the chemical equations
3.
Enthalpy diagram

Same 3 ways to Representing Endothermic Reactions
1.
A balanced chemical equation that indicates the amount of heat that is absorbed or released by the reaction it represents. Because heat is absorbed the heat term is on the reactant side. o
2.
You can also put enthalpy as a separate expression beside the chemical equations
3.
Enthalpy diagram
Stoichiometry and Thermochemical Equations
Enthalpy of reaction is linearly dependant on the quantity of products. If the amount of products doubles the enthalpy change doubles.