chapter 6 energy general, organic, & biological chemistry janice gorzynski smith

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CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice Gorzynski Smith

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CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice Gorzynski Smith. CHAPTER 6: Energy. Learning Objectives: Definition of Energy, Kinetic Energy, Potential Energy Heat transfer in reactions Enthalpy Exothermic and endothermic Energy unit conversions and calculations - PowerPoint PPT Presentation

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Page 1: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

CHAPTER 6Energy

General, Organic, & Biological Chemistry

Janice Gorzynski Smith

Page 2: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

2

CHAPTER 6: Energy

Smith. General Organic & Biolocial Chemistry 2nd Ed.

Learning Objectives: Definition of Energy, Kinetic Energy, Potential Energy

Heat transfer in reactions

Enthalpy

Exothermic and endothermic

Energy unit conversions and calculations

Bond Strength

Energy diagrams

How to change the rate of a reaction

Catalysts

Equilibrium: definition and calculations

Re-establishing equilibrium and Le Chatlier’s principle

Page 3: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

3

Energy Definition of Energy

Smith. General Organic & Biolocial Chemistry 2nd Ed.

Total Energy

Potential Energy

Kinetic Energy

= +

Energy is the capacity to do work.

Potential energy is stored energy.

The law of conservation of energy states that the total energy in a system does not change. Energy cannot be created or destroyed.

Kinetic energy is the energy of motion.

Page 4: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

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Energy Kinetic Energy

Smith. General Organic & Biolocial Chemistry 2nd Ed.http://www.petervaldivia.com/technology/energy/

http://scienceisntscary.wordpress.com/tag/kinetic-energy/

Kinetic Energy (KE)

Energy of motion

KE = ½mv 2

Page 5: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

5

Energy Potential Energy

Smith. General Organic & Biolocial Chemistry 2nd Ed.

Potential Energy

= Stored energy

Exists in natural attractions and repulsions

Chemical Energy• PE possessed by chemicals

• Stored in chemical bonds• Breaking bonds requires energy• Forming bonds releases energy

PE

Reactants Products

Lower PEFavorable

Stable

Higher PEUnfavorable

UnstableR

P

P

Page 6: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

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Energy Units of Energy

Smith. General Organic & Biolocial Chemistry 2nd Ed.

•A calorie (cal) is the amount of energy needed to raise the temperature of 1 g of water by 1 oC.

•A joule (J) is another unit of energy.

1 cal = 4.184 J

•Both joules and calories can be reported in the larger units kilojoules (kJ) and kilocalories (kcal).

1,000 J = 1 kJ 1,000 cal = 1 kcal

1 kcal = 4.184 kJ

Page 7: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

7

Energy Example: Energy in a Gummy Bear

Smith. General Organic & Biolocial Chemistry 2nd Ed.

A gummy bear is 9.000 Calories (nutritional calories). How much energy is stored in a gummy bear in units of Joules?

9.000 Cal = 9.000 kcal x 1000 cal = 9000. cal

9000. cal x 4.184 J = 37660. J = 37.66 kJ

1 kcal

1 cal

Gummy Bear Video: https://www.youtube.com/watch?v=6YWGnfnEmgM&src_vid=Jzoi7dJAiSc&feature=iv&annotation_id=annotation_713078

Page 8: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

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Energy Breaking and Forming Bonds

Smith. General Organic & Biological Chemistry 2nd Ed.

ClCl

To cleave this bond, 58 kcal/mol must be added.

H = +58 kcal/molEndothermic To form this bond, 58

kcal/mol is released.H = −58 kcal/mol

Exothermic

Breaking bonds requires energyForming bonds releases energy

H is the energy absorbed or released in a reaction; it is called the heat of reaction orthe enthalpy change.

Page 9: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

9

Energy Enthalpy Change & Bond Dissociation Energy

Smith. General Organic & Biological Chemistry 2nd Ed.

The bond dissociation energy is the H for breakinga covalent bond by equally dividing the e− between the two atoms.

Bond dissociation energies are positive values, because bond breaking is endothermic (H > 0).

Bond formation always has negative values, because bond formation is exothermic (H < 0).

H H H + H

H + H H H

H = +104 kcal/mol

H = −104 kcal/mol

Page 10: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

10

Energy Bond Strength

Smith. General Organic & Biological Chemistry 2nd Ed.

The stronger the bond, the higher its bond dissociation E.

H indicates the relative strength of the bonds broken and formed in a reaction:

• H negative: Exothermic reaction: more energy required to break products then reactant bonds: products have stronger bonds.

• H positive: Endothermic reaction: less energy required to break products then reactant bonds: products have weaker bonds.

Page 11: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

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Energy Endothermic & Exothermic

Smith. General Organic & Biological Chemistry 2nd Ed.

Page 12: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

12

Reactions Energy Diagrams

Smith. General Organic & Biological Chemistry 2nd Ed.

The orientation of the two molecules must be correct as well.

For a reaction to occur, two molecules must collidewith enough kinetic energy to break bonds.

Page 13: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

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Reactions Energy Diagrams

Smith. General Organic & Biological Chemistry 2nd Ed.

Ea, the energy of activation, is the difference in energy between the reactants and the transition state. It can be thought of as the energy barrier that must be overcome for the reaction to occur.

Page 14: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

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Reactions Energy Diagrams

Smith. General Organic & Biological Chemistry 2nd Ed.

H is positive, the reaction is endothermic:

H is negative, the reaction is exothermic:

When the Ea is high, few molecules have enough energy to cross the energy barrier, and the reaction is slow.

When the Ea is low, many molecules have enough energy to cross the energy barrier, and the reaction is fast.

Page 15: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

E

Reactants

ProductsEXOTHERMIC

ENDOTHERMIC

Heat released

Heat absorbed

ENDOTHERMICHeat + Reactants Products

Products have weaker bonds and a higher energy then Reactants.

Heat is absorbed by the system.ΔE + ΔH +

EXOTHERMICReactants Products + heat

Products have stronger bonds and a lower energy then Reactants.

Heat is released by the system.

ΔE - ΔH -

PE increasesas bonds

break

PE decreasesas bonds

form

Summary Energy & Reactions

Page 16: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

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Reactions Ex: Splitting Water

Smith. General Organic & Biological Chemistry 2nd Ed.

Requirments: Very Endothermico Need a minimum of 1.23 V to split water

o Kinetically infrared light could do this, but the reaction is very slow

o The potential really needs to be at least 3.0 V to utilize the full spectrum of light

Page 17: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

17

Reactions Rates of Reactions

Smith. General Organic & Biological Chemistry 2nd Ed.

Increasing the concentration of the reactants:•Increases the number of collisions•Increases the reaction rate

Increasing the temperature of the reaction:•Increases the kinetic energy of the molecules•Increases the reaction rate

A catalyst is a substance that speeds up the rate of a reaction and can be recovered unchanged.

•Catalysts lower Activation Energy, Ea.

Page 18: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

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Reactions Catalysts

Smith. General Organic & Biological Chemistry 2nd Ed.

•The uncatalyzed reaction (higher Ea) is slower.

•The catalyzed reaction (lower Ea) is faster.

H is the same for both reactions.

Page 19: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

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Reactions Catalysts: Photosystem II

Smith. General Organic & Biological Chemistry 2nd Ed.

PQ + H2O --> PQH2 + O2 (g)

The overall reaction of Photosystem II is the oxidation of water and the reduction of plastoquinone.

Page 20: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

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Reactions Equilibrium

Smith. General Organic & Biological Chemistry 2nd Ed.

A reversible reaction can occur in either direction.

CO(g) + H2O(g) CO2(g) + H2(g)

The forward reaction proceeds to the right.

The reverse reactionproceeds to the left.

•The system is at equilibrium when the rate of the forward reaction equals the rate of the reverse reaction.

•The net concentrations of reactants and products do not change at equilibrium.

Page 21: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

21

Reactions Equilibrium

Smith. General Organic & Biological Chemistry 2nd Ed.

a A + b B c C + d D

equilibriumconstant = K =

[C]c [D]d

[A]a [B]b=

[products][reactants]

The relationship between the concentration of the products and the concentration of the reactants is the equilibrium constant, K.

*Brackets, [ ], are used to symbolize concentration in moles per liter (mol/L).

Page 22: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

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Reactions Equilibrium

Smith. General Organic & Biological Chemistry 2nd Ed.

N2(g) + O2(g) 2 NO(g)

equilibriumconstant

= K =[N2] [O2]

[NO]2

*The coefficient becomes the exponent.

Page 23: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

23

Reactions Equilibrium

Smith. General Organic & Biological Chemistry 2nd Ed.

HOW TO Calculate the Equilibrium Constant for a Reaction

A2 + B2 2 AB

Step [1]

Write the expression for the equilibriumconstant from the balanced equation.

[AB]2

[A2][B2]K =

Step [2]

Substitute the given concentrations inthe equilibrium expression and calculate K.

[AB]2

[A2][B2]K = =

[0.50]2

[0.25][0.25] =0.25

0.0625= 4.0

Page 24: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

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Reactions Le Châtelier’s Principle

Smith. General Organic & Biological Chemistry 2nd Ed.

If a chemical system at equilibrium is disturbed orstressed, the system will react in a direction thatcounteracts the disturbance or relieves the stress.

Some of the possible disturbances:

1) Concentration changes

2) Temperature changes

3) Pressure changes

Page 25: CHAPTER 6 Energy General, Organic, & Biological Chemistry Janice  Gorzynski Smith

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Reactions Le Châtelier’s Principle

Smith. General Organic & Biological Chemistry 2nd Ed.