Thermochemistry The study of heat energy changes in chemical reactions. Importance: 1. Safety considerations. KABOOM! 2. Heat energy used for work. Examples: Burn methane to heat home. Burn gasoline to power car. Burn coal to produce electricity. HW 12-1, #1 Kabom link Bozeman energy transformation

Turbine Generator - Generating electric current by moving a magnet rapidly around coiled copper wire Phet Electromagnetic Induction

How does the chemical energy from burning coal generate electricity? Heat Energy from burning coal → water to steam → steam pushes turbine blades to generate electricity

What is Energy? Energy = capacity to do work Work = Force x distance “working” defn of energy = capacity to make objects move

1st Law of Thermodynamics Energy can neither be created nor destroyed! Energy can only be transformed from one form to another. Also known as the Conservation of Energy Phet skateboard link Bozeman video link

How badly do you want the “Free Stuff?” What could POTENTIALLY happen?

Potential Energy (PE) Stored energy due to position OR chemical composition. “Position” examples:

Potential energy transformed into . . .

Kinetic Energy(KE) Energy of Motion BUNGEE JUMP LINK

Potential Energy (PE) due to Chemical Composition Trinitrotoluene Hi PE (Weak bonds, unstable) Lo PE (Strong bonds, stable) NO2 bonds are weak; Atoms rearrange to form N2, CO and CO2 gases with strong bonds (+ Carbon)

Potential TO become . . .

Kinetic Energy (KE)- molecules with higher KE move faster Product Molecules have Lower PE but much Higher Kinetic energy molecules FIREBALL LINK

HW 12-1, #2 4 2 10 Location PE UNITS KE UNITS TOTAL ENERGY 1 10 2 6 3 2 6 3 8 4 2 10

The Ethanol Cannon: Example of First Law in Action . . Converting Stored Potential Chemical Energy into Kinetic Energy!

C2H5OH + O2 → C2H5OH + O2 have potential energy due to HW 12-1, #3A,3B C2H5OH + O2 → C2H5OH + O2 have potential energy due to What type of reaction pattern is this? ANS: Combustion of a hydrocarbon What are the products? ANS: CO2 + H2O CHEMICAL COMPOSITION

The reaction between ethanol and oxygen is thermodynamically favorable, yet nothing is happening, why? The collisions between molecules don’t have enough energy to overcome the activation barrier. What is happening What we want to happen HW 12-1, #3C

Meet Mr. Tesla Coil! As electricity travels across the gap between the two nails it will heat the gas molecules past the Ea

How does the potential energy (PE) and kinetic energy (KE) of the reactant ethanol and oxygen molecules compare to the PE and KE of the product CO2 and H2O molecules? Reactants Products Hi PE Lo KE Lo PE Hi KE

Since final product molecules CO2 and H2O have lower potential energy but higher kinetic energy the difference in energy has been released as heat and light. Link to gases phet

Extra KE pushes cork across room! Hot gases have higher kinetic energy push outwards against the cork, sending it across the room. Extra KE pushes cork across room! Cannon video link

HW 12-1, #3D REACTANTS PRODUCTS KE KE PE KE PE KE PE PE PE KE KE KE

HW 11-4, #3E Lo Hi Lo Hi UNSTABLE STABLE WEAKER STRONGER Property REACTANTS PRODUCTS PE KE STABLE/ UNSTABLE STRONGER BONDS/ WEAKER BONDS Lo Hi Lo Hi UNSTABLE STABLE WEAKER STRONGER

Reaction Profile Diagram for Ethanol Cannon HW 11-4, #3F Hi PE, Lo KE Lo PE, Hi KE