Thermody-nizzle-amicsThermody-nizzle-amics

A (Josh)^2 ProductionA (Josh)^2 Production

Heating ShindigHeating Shindig

Amount of energy needed to change a Amount of energy needed to change a given substance a given temperature given substance a given temperature depends on;depends on; The mass you are heating (how much)The mass you are heating (how much) It’s specific heat (how well it can absorb It’s specific heat (how well it can absorb

energy)energy) Some random stuff: Specific heat changes from Some random stuff: Specific heat changes from

phase to phase; Water has high specific heat phase to phase; Water has high specific heat (4.186 J/g*K); Metals have low specific heat(4.186 J/g*K); Metals have low specific heat

Q = MCQ = MCTT

Shifting Phaz0rzShifting Phaz0rz

Phase change occurs at a constant Phase change occurs at a constant temperaturetemperature

How much energy is required to change How much energy is required to change a substance from one phase or another a substance from one phase or another depends on:depends on: The mass of the substance presentThe mass of the substance present A constant called Heat of fusion (S <->L) or A constant called Heat of fusion (S <->L) or

heat of vaporization (L<->G)heat of vaporization (L<->G) Q = KMQ = KM

Sample Heating Curve of Sample Heating Curve of CaliforniumCalifornium

Chemical SystemsChemical Systems

Chemical systems simply refer to Chemical systems simply refer to the actual chemicals (the system) the actual chemicals (the system) and it’s surroundingsand it’s surroundings

System

Surroundings

Enthalpy is Hot Enthalpy is Hot (sometimes)(sometimes)

Enthalpy refers to how much energy Enthalpy refers to how much energy is stored within a chemical systemis stored within a chemical system

When a reaction occurs, there is a When a reaction occurs, there is a change in enthalpy, change in enthalpy, HH A positive change in enthalpy, A positive change in enthalpy, H > 0, means H > 0, means

that energy is entering the system. Such a that energy is entering the system. Such a process is known as endothermic.process is known as endothermic.

A negative change in enthalpy, A negative change in enthalpy, H < 0, means H < 0, means that energy is leaving the system. This is an that energy is leaving the system. This is an exothermic process.exothermic process.

But wait…But wait…

Q: If the energy in the system is Q: If the energy in the system is going down during an exothermic going down during an exothermic process, why does it seem process, why does it seem exothermic processes make things exothermic processes make things hot?hot?

A: Cuz I said so… and because A: Cuz I said so… and because you’re in the surroundings gaining you’re in the surroundings gaining the energy lost from the system.the energy lost from the system.

How to Find Change in How to Find Change in EnthalpyEnthalpy

Bond EnergiesBond EnergiesHeat of FormationHeat of FormationHess’ LawHess’ Law

Bond EnergiesBond Energies

Given a table of bond energies, Given a table of bond energies, find the total bond energy of the find the total bond energy of the products and of the reactants. products and of the reactants. Remember coefficientsRemember coefficients

H = H = ∑Bond Energy∑Bond EnergyReactantsReactants

- ∑Bond Energy- ∑Bond EnergyProductsProducts

Note: this is the only one where it’s Note: this is the only one where it’s reactants minus productsreactants minus products

Heat of FormationHeat of Formation

This one’s even easier. First find the This one’s even easier. First find the heat of formation of the products heat of formation of the products and reactants (It’ll be given, and reactants (It’ll be given, unless…)unless…)

All elemental substances (like OAll elemental substances (like O22, , Fe, etc.) have Fe, etc.) have HH°°FF = 0 J = 0 J

To find enthalpy;To find enthalpy;

H H °° rxnrxn = = ∑ ∑ HH°°FF ProductsProducts - - ∑ ∑ HH°°FF ReactantsReactants

My Homedawg HessMy Homedawg Hess

Hess’ Law: If a reaction is the sum of Hess’ Law: If a reaction is the sum of two or more other reactions, the two or more other reactions, the enthalpy change for the overall enthalpy change for the overall process is the sum of the enthalpy process is the sum of the enthalpy changes for the constituent changes for the constituent reactions. Sweet.reactions. Sweet.

Let’s make methane!?!Let’s make methane!?!

Use these reactions to find Use these reactions to find HH°°FF of of CHCH44

C + OC + O22 CO CO2 2 H = -393.5 kJH = -393.5 kJ

HH22 + ½ O + ½ O22 H H22O O H = -285.8 kJH = -285.8 kJ

CHCH44 + 2O + 2O22 CO CO2 2 + 2H+ 2H22O O H = -890.3 kJH = -890.3 kJ

Stop defying Entropy; go Stop defying Entropy; go combust right now!combust right now!

Entropy is a measure of disorder in a Entropy is a measure of disorder in a system.system.

It is measured by how much energy a It is measured by how much energy a substance has compared to its absolute substance has compared to its absolute temperature. S = q/T (J/(mol * K))temperature. S = q/T (J/(mol * K))

Chaotic things have greater entropy; gas Chaotic things have greater entropy; gas has more entropy than liquid, and liquid has more entropy than liquid, and liquid more than solid. Stone’s hair has lots of more than solid. Stone’s hair has lots of entropy.entropy.

Potentially useful: Potentially useful: S S rxnrxn = = ∑ ∑ SSProductsProducts - - ∑ ∑ SSReactantsReactants

Hippopotami can cause increases in entropy

How the Universe WorksHow the Universe Works

Everything moves towards maximum Everything moves towards maximum entropy and minimum enthalpyentropy and minimum enthalpy

Basically, everything wants to Basically, everything wants to spread its matter and energy across spread its matter and energy across the universethe universe

22ndnd Law of Thermodynamics: The Law of Thermodynamics: The Entropy of the Universe is always Entropy of the Universe is always increasing. (don’t worry about the increasing. (don’t worry about the others)others)

The work of a True Hero, J. The work of a True Hero, J. Willard Gibbs.Willard Gibbs.

S S UniverseUniverse = = S S SystemSystem + + S S SurroundingsSurroundings

S S UniverseUniverse = = S S SystemSystem - - H H System System /T/T

-T-TS S UniverseUniverse = = H H System System - T- TS S SystemSystem

-T-TS S UniverseUniverse is given as is given as G, change in Gibbs G, change in Gibbs free energy. Since free energy. Since S S UniverseUniverse is positive if is positive if G G is negative, if is negative, if G < 0, than a reaction is G < 0, than a reaction is spontaneous (IE product favoring)spontaneous (IE product favoring)

Summary: Summary: G G = = H H System System - T- TS S SystemSystem

Possible Reaction TypesPossible Reaction Types

Exothermic and increasing entropy; Exothermic and increasing entropy; always spontaneousalways spontaneous

Endothermic and increasing entropy; Endothermic and increasing entropy; spontaneous at higher temperaturesspontaneous at higher temperatures

Exothermic and decreasing in Exothermic and decreasing in entropy; spontaneous at lower entropy; spontaneous at lower temperaturestemperatures

Endothermic and decreasing in Endothermic and decreasing in entropy; never spontaneousentropy; never spontaneous

Gibbs and Q and KGibbs and Q and K

Sorry, no proof this timeSorry, no proof this time

G = G = GG° ° + RT lnQ+ RT lnQ

R = 8.314 J/ (Mol * K)R = 8.314 J/ (Mol * K)

If reaction is at equilibrium, If reaction is at equilibrium, G = 0 soG = 0 so

GG° ° = -RT lnK= -RT lnK

ApplicationsApplications

Throwing Hot Blocks of Metal Throwing Hot Blocks of Metal into Water or Jello or maybe into Water or Jello or maybe EthanolEthanol

Remember energy is conserved Remember energy is conserved and the system will reach and the system will reach equilibrium at a common equilibrium at a common temperaturetemperature

Basic formBasic form

MM11CC11(T(Tff – T – Ti1i1) = M) = M22CC22(T(Ti2i2 – T – Tff) )

CalorimetersCalorimeters Calorimeters measure reaction enthalpy by Calorimeters measure reaction enthalpy by

recording change in surroundings.recording change in surroundings. Calorimeters will often have their own Calorimeters will often have their own

specific heat, but it factors in their mass so specific heat, but it factors in their mass so Q = C Q = C T for calorimeters. It is assumed T for calorimeters. It is assumed they don’t melt.they don’t melt.

Enthalpy is found by measuring the change Enthalpy is found by measuring the change in temperature of the calorimeter, in temperature of the calorimeter, calculating its increase in energy, and calculating its increase in energy, and comparing that to how much stuff was comparing that to how much stuff was reacted.reacted.

Chipotle Burritos Have Lots of Calories. Gana can eat three of them. Gana is a true hero just like J. Willard Gibbs.

Melting/Freezing and Melting/Freezing and Evaporation/Condensation Evaporation/Condensation PointsPoints

All phase changes are increase in All phase changes are increase in entropy and endothermic or vice entropy and endothermic or vice versa. The reaction has no favored versa. The reaction has no favored side when side when G is zero, therefore G is zero, therefore that temperature is the that temperature is the melting/freezing etc. point. From melting/freezing etc. point. From the earlier equationthe earlier equation

TTphase changephase change = = HHphase changephase change / / SSphase changephase change

FINFIN