Thermodynamics Topic 7 Chemistry Semester 2 THIS POWER POINT IS BEST VIEWED IN SLIDE SHOW MODE: Select Slide Show from the top menu, then Select Current Slide

Thermodynamics basics worksheet Obtain and complete the thermodynamics basics worksheet as you work through this power point. Show Ms. Cobler once you have finished.

Energy Transfer

Law of conservation of energy Energy is not created or destroyed during any normal physical or chemical process. Energy can be converted between different forms A look at how energy can be converted between forms: https://phet.colorado.edu/en/simulation/energy-forms-and- changes Select Energy Systems and Select Energy Symbols Select the bicycle, and the curly lightbulb. 1. What type of energy does the person riding the bicycle use? Define this type of energy. 2. The energy from question one is mainly converted into what type of energy? Define this type of energy. 3. The energy from question two is mainly converted into what type of energy? Define this type of energy. 4. The energy from question three is mainly converted into what type of energy? Define this type of energy. You may want to create flash cards for these 4 energy types as well as Kinetic and Thermal energies.

Energy Transfer Energy can move into, out of and through a system in 3 ways Radiation Convection Conduction

Radiation When energy is radiated, it can travel from one object to another via rays—like light or infrared & UV waves. Sunlight is energy transferred by radiation

Convection Within a system, heat energy can flow as warm (less dense) fluids rise and cooler (more dense) fluids sink This happens in lava lamps! And with lava beneath earth’s crust

Conduction When object heat spreads when molecules vibrate against each other. Pan handles become too hot to handle when molecules spread heat to each other

Try with a neighbor: How is heat moving? Radiation Convection Conduction

Energy Changes in Chemical Reactions https://www.youtube.com/watch?v=GQkJI-Nq3Os https://www.youtube.com/watch?v=rdCsbZf1_Ng

Measuring and Diagraming Energy in chemical reactions

Chemical Energy aka Chemical Potential Energy, aka bond energy Chemical Energy is energy stored in the bonds between atoms. Energy is added (and stored) when breaking a bond Energy is released when creating a bond.

Chemical Energy During any chemical reaction, some bonds are broken and others are newly formed. This means total chemical energy can go up as energy is absorbed (endothermic)… …or go down as energy is released (exothermic).

Heat of reaction Whether total energy goes up or down, the change is called “heat of reaction” and symbolized ΔH +ΔH -ΔH

As we will see, real Energy Diagrams can be appear more complicated

Enthalpy Enthalpy is defined as the total energy content of an object. This energy includes: heat (thermal energy) potential (such as phase energy) and chemical (bond energy) --new! H (delta H) represents Enthalpy , ETh ECh EPh

Imagine the reaction: This reaction can occur in 2 stages: One bond breaks: Another bond forms:

The bond-breaking step is endothermic The bond-forming step is exothermic

In reality The bond breaking and forming can happen simultaneously. After forming this, the reaction completes

Overall we get a potential energy diagram with a hill to climb over.

Real reactions may take place in one step, but there’s always a hill to climb

True Potential energy diagrams may show the hill like this: This partially formed molecule is called the activated complex

The energy needed to get to the top of the hill is called activation energy

The net drop in energy is the heat of reaction

Heat of reaction may also be an increase in energy

Many reactions are reversible!

The activation energy for a backward reaction would be different Reverse Activation Energy

Complete the Energy Diagram worksheet as you watch this video, you need to know the parts of this diagram.

Complete the Energy Diagram worksheet Show Ms Complete the Energy Diagram worksheet Show Ms. Cobler when you are finished Sketch an LOL diagram (just diagraming chemical potential energy) on the back of this work sheet. Things to think about Is the reaction endothermic or exothermic? Which of these means energy is leaving the system which of these means energy is being absorbed by the system? Do the products or reactants have more energy? Reactants Products

Calculating Heat/Energy Changes

Heat of formation (ΔHfo) A special kind of heat of reaction Heat of formation is the energy change when making a compound from its elements. Ex: H2(g) + ½O2(g) → H2O(g) Ex: 0kj 0kj -241.8kj Ex: [-241.8 kj] – [0 kj + (½ * 0 kj)] = -241.8kj The ΔHfo for this reaction is -242kJ/mol. This number is negative, meaning this is an exothermic reaction. The reaction releases 242kJ of energy for each mole of water made. Equation: ΔHrnx = ∑ΔHfo (products) - ∑ΔHfo (reactants) Add up heats for all the products and subtract heats for all the reactants. Use coefficients to multiply the ΔHfo Make sure you have the correct phase!

ΔHrnx = ∑ΔHfo (products) - ∑ΔHfo (reactants) What you need to know: Look up each ΔHfo from a table Multiply each by its coefficient Add together all products. Add together all reactants. Subtract PRODUCTS – REACTANTS.

Heat of reaction worksheet Obtain and complete the Heat of Reactions worksheet. Answers have been included. Show Ms. Cobler once you have finished.

Hess’s Law

Hess’s Law Example Mobile phones are being developed that can be powered by methanol. Methanol can be made by a two-stage process. In the first stage, methane is reacted with steam to produce a mixture of carbon monoxide and hydrogen. CH4(g) + H2O(g) → CO(g) + 3H2(g) Data:   CO(g) + ½O2(g) → CO2(g) ΔH = −283 kJ mol–1 H2(g) + ½O2(g) → H2O(g) ΔH = −242 kJ mol–1 CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) ΔH = −803 kJ mol–1

Hess’s Law Example: Step 1 – Identify components Mobile phones are being developed that can be powered by methanol. Methanol can be made by a two-stage process. In the first stage, methane is reacted with steam to produce a mixture of carbon monoxide and hydrogen. CH4(g) + H2O(g) → CO(g) + 3H2(g) Data:   CO(g) + ½O2(g) → CO2(g) ΔH = −283 kJ mol–1 H2(g) + ½O2(g) → H2O(g) ΔH = −242 kJ mol–1 CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) ΔH = −803 kJ mol–1 You need to make this equation From these equations

Hess’s Law Example: Step 2 – Reverse Equations to get all products and reactants on the correct side. Mobile phones are being developed that can be powered by methanol. Methanol can be made by a two-stage process. In the first stage, methane is reacted with steam to produce a mixture of carbon monoxide and hydrogen. CH4(g) + H2O(g) → CO(g) + 3H2(g) Data: CO(g) + ½O2(g) → CO2(g) ΔH = −283 kJ mol–1 CO2(g) → CO(g) + ½O2(g) ΔH = 283 kJ mol–1 H2(g) + ½O2(g) → H2O(g) ΔH = −242 kJ mol–1 H2O(g) → H2(g) + ½O2(g) ΔH = 242 kJ mol–1 CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) ΔH = −803 kJ mol–1 Water, hydrogen, and carbon monoxide need to be reversed The equations end up looking like this. The delta H also changes from negative to positive.

Hess’s Law Example: Step 3 – Multiply equations to make coefficients match the original equation. Mobile phones are being developed that can be powered by methanol. Methanol can be made by a two-stage process. In the first stage, methane is reacted with steam to produce a mixture of carbon monoxide and hydrogen. CH4(g) + H2O(g) → CO(g) + 3H2(g) Data:  CO2(g) → CO(g) + ½O2(g) ΔH = 283 kJ mol–1 H2O(g) → H2(g) + ½O2(g) ΔH = 242 kJ mol–1 3H2O(g) → 3H2(g) + 1½O2(g) ΔH = 726 kJ mol–1 CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) ΔH = −803 kJ mol–1 CH4(g), H2O(g), CO(g) all have the correct coefficients Only the H2(g) needs to be multiplied. You must multiply the whole equation. Including the delta H.

Hess’s Law Example: Step 4 – Line everything up and cancel out like compounds and elements. Mobile phones are being developed that can be powered by methanol. Methanol can be made by a two-stage process. In the first stage, methane is reacted with steam to produce a mixture of carbon monoxide and hydrogen. CH4(g) + H2O(g) → CO(g) + 3H2(g) Data:   CO2(g) → CO(g) + ½O2(g) ΔH = 283 kJ mol–1 3H2O(g) → 3H2(g) + 1½O2(g) ΔH = 726 kJ mol–1 CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) ΔH = −803 kJ mol–1 1 Molecule of CO2(g) Can be found on the reactants and products side of these equations. These cancel out. 2 molecules of O2(g) Can be found on the reactants and products side of these equations [1½ + ½ = 2]. These cancel out. We have just one last thing to get rid of from the products side of the last equation, 2H2O(g). But wait, don’t we need H2O(g)? Notice how our equation needs 1 H2O(g) but our highlighted H2O(g) has a 3 as a coefficient, subtract 2H2O(g) from 3H2O(g) and you are left with 1 H2O(g).

Hess’s Law Example: Step 5 – Combine the remainder of the equations. Mobile phones are being developed that can be powered by methanol. Methanol can be made by a two-stage process. In the first stage, methane is reacted with steam to produce a mixture of carbon monoxide and hydrogen. CH4(g) + H2O(g) → CO(g) + 3H2(g) Data:   → CO(g) ΔH = 283 kJ mol–1 H2O(g) → 3H2(g) ΔH = 726 kJ mol–1 CH4(g) → ΔH = −803 kJ mol–1 Answer CH4(g) + H2O(g) → CO(g) + 3H2(g) ΔH = [283 + 726 + (-803)] = 206 kJ mol–1

Hess’s Law worksheet Obtain and complete the Hess’s Law worksheet. Answers have been included. Show Ms. Cobler once you have finished.