Chemical energy

Summary for Chapter 6Chemical Energy

3 ways of determining heat of reactions

2 ways of presenting heat of reactions

Hess law

Bond energies

In a lab

In an equation

In an energy diagram

Click below

Hess's law

Example #3

Example #4

What is Hess's law

Example #1

Example #2

Click to watch the videosClickto watch it in full screen.Both types of calculations will lead to the same result.

Calculations with energy term in the equation.

Calculations with energy term outside the equation.

Bond Energy

Extra review on structural formulas

Bond energies (p. 237)

Example #1

Example #2

Click to watch the videosClickto watch it in full screen.

Examples

Answer

With the energy bond method,you can determine bothheat of reactionandactivation energy!

Lab

Example #1

Example #2

Click to watch the videosClickto watch it in full screen.

Calculations

Heat of reaction in an equation

Endothermic reaction

Exothermic reaction

Example (click on picture)

Example (click on picture)

Energy diagram

Endothermic reaction (click on picture)

Exothermic reaction (click on picture)

Energy diagram with or without the activated complex

Endothermic reaction

With the activated complex

Without the activated complex

Enthalpy of the reactants (whose value is usually not specified)

Activated complex where everything exists as individual atoms It is the most unstable form!

Activation energy (also the energy from breaking all the bonds within the reactants)

Delta H / difference in enthalpy / heat of reaction Enthalpy of the products is higher than the enthalpy of the reactants Meaning more energy is needed to start the reaction than released -> Endothermic reaction

Enthalpy of the products (whose value is usually not specified)

Enthalpy of the reactants (whose value is usually not specified)

Delta H / difference in enthalpy / heat of reaction Enthalpy of the products is higher than the enthalpy of the reactants Meaning more energy is needed to start the reaction than released -> Endothermic reaction

Enthalpy of the products (whose value is usually not specified)

Exothermic reaction

With the activated complex

Without the activated complex

Enthalpy of the reactants (whose value is usually not specified)

Activated complex where everything exists as individual atoms It is the most unstable form!

Activation energy (also the energy from breaking all the bonds within the reactants)

Delta H / difference in enthalpy / heat of reaction Enthalpy of the products is lower than the enthalpy of the reactants Meaning less energy is needed to start the reaction than released -> Exothermic reaction

Enthalpy of the products (whose value is usually not specified)

Enthalpy of the reactants (whose value is usually not specified)

Delta H / difference in enthalpy / heat of reaction Enthalpy of the products is lower than the enthalpy of the reactants Meaning less energy is needed to start the reaction than released -> Exothermic reaction

Enthalpy of the products (whose value is usually not specified)