And Chemistry? Joules or calories. Evidence of Energy Motion Heat Light Sound

andand Chemistry? Chemistry?

Joules or calories Joules or calories

Joules or calories Joules or calories

Evidence of EnergyEvidence of Energy

MotionMotion HeatHeat LightLight SoundSound

Energy UnitsEnergy Units

joulejoule ≡≡ energy exerted by a force of one Newton acting to move an energy exerted by a force of one Newton acting to move an object through a distance of one meter (SI unit)object through a distance of one meter (SI unit)

caloriecalorie ≡ ≡ the amount of energy required to heat 1 gram of water 1the amount of energy required to heat 1 gram of water 1ooCC

CalorieCalorie = 1000 calories = 1000 calories

1Joule = 0.2390 cal1Joule = 0.2390 cal

How much is 1 Joule of energy?How much is 1 Joule of energy?

the energy required to lift a small apple one the energy required to lift a small apple one meter straight up.meter straight up.

the energy released as heat by a quiet the energy released as heat by a quiet person, every hundredth of a second.person, every hundredth of a second.

the kinetic energy of an adult human moving the kinetic energy of an adult human moving a distance of about 6 inches every second.a distance of about 6 inches every second.

Types of EnergyTypes of Energy ChemicalChemical HeatHeat LightLight SoundSound ElectricalElectrical MagneticMagnetic MotionMotion NuclearNuclear

ChemicalChemical

ThermalThermal

ElectromagneticElectromagnetic

KineticKinetic NuclearNuclear

AcousticAcoustic

LightLight

GravitationalGravitational

EE

Energy TransformationsEnergy Transformations

ChemicalChemical

ThermalThermal

ElectromagneticElectromagnetic

KineticKinetic NuclearNuclear

AcousticAcoustic

LightLight

GravitationalGravitational

EE

Energy TransformationEnergy Transformation

Either or EnergyEither or Energy

Energy can be sorted into one of two Energy can be sorted into one of two categories – categories –

eithereither– kinetickinetic (the “doing the work” phase) (the “doing the work” phase)

oror– potentialpotential (the getting ready to do work or the (the getting ready to do work or the

“stored” phase)“stored” phase)

Energy examplesEnergy examples

Potential

Mechanical Energy

and

?

Potential

Mechanical Energy

and

?

Kinetic

Mechanical Energy

and

?

Kinetic

Mechanical Energy

and

?

Forms of Kinetic Energy

Electrical – movement of electrons

Electromagnetic – moving electro magnetic waves (light, x-rays, gamma rays, radio waves)

Thermal – vibrations and movements of particles in a substance

Mechanical – movement of objects

Sound – movement of particles as energy travels through a medium

Forms of Kinetic Energy

Electrical – movement of electrons

Electromagnetic – moving electro magnetic waves (light, x-rays, gamma rays, radio waves)

Thermal – vibrations and movements of particles in a substance

Mechanical – movement of objects

Sound – movement of particles as energy travels through a medium

Potential Energy

Chemical – energy stored in the bonds of molecules

Stored mechanical – energy stored in an object based on its position relative to some reference state (i.e. a wound springs, a stretched rubber band, a boulder perched on the edge of a cliff)

Nuclear – energy stored in nucleus of an atom

Gravitational – energy stored based on relative position of two objects

Potential Energy

Chemical – energy stored in the bonds of molecules

Stored mechanical – energy stored in an object based on its position relative to some reference state (i.e. a wound springs, a stretched rubber band, a boulder perched on the edge of a cliff)

Nuclear – energy stored in nucleus of an atom

Gravitational – energy stored based on relative position of two objects

How much energy is stored in How much energy is stored in glucose?glucose?

CC66HH1212OO66

1 gram of carbohydrate releases 4 Calories when burned

1 gram of fat releases 9 Calories when burned

Chemical EnergyChemical Energy

Energy is stored in the bonds between Energy is stored in the bonds between atoms.atoms.

When chemical reactions occur, bonds are When chemical reactions occur, bonds are broken and formed.broken and formed.

The amount of energy released / absorbed The amount of energy released / absorbed during a chemical reaction can be measured during a chemical reaction can be measured and calculated from the bond energiesand calculated from the bond energies

Bond EnergyBond Energy

Energy is absorbed by atoms when their bonds break.

(+ΔH) ≡ heat of bond breaking

Energy is released when bonds form between atoms.

(-ΔH) ≡ heat of bond formation

Bond Energy - AnalogyBond Energy - Analogy

Imagine stretching a rubber band until it breaks. You must do work to stretch the band because the tension in the band opposes your efforts. You lose energy; the band gains it. Something similar happens when bonds break in a chemical reaction.

The energy required to break the bonds is absorbed from the surroundings.


BondEnergy (kJ/mol)

H - H 436

C - H 413

N - H 393

436 kJ is stored in H-H

436 kJ is released when H-H is broken

The higher the bond energy, the more work is required to break the bond, the more stable it is


BondEnergy (kJ/mol)

BondEnergy (kJ/mol)

H - H 436 N - N 160

C - H 413 N = O 631

N - H 393 N triple N 941

P - H 297 N - O 201

C - C 347 N - P 297

C - O 358 O - H 464

C - N 305 O - S 265

C - Cl 397 O - Cl 269

C = C 607 O - O 204

C = O 805 C - F 552

O = O 498 C - S 259


Energy is absorbed when bonds break.

Energy is released when bonds form.

Energy is absorbed or released when the heat capacities of the products and reactants differ.

Calculating Energy of a ReactionCalculating Energy of a Reaction

H2 + Cl2 2HCl

Breaking H bond = 436 kJ/mol

Breaking Cl bond = 242 kJ/mol

H-Cl bond forming = -431 kJ/mol

Reactions and EnergyReactions and Energy

If heat is generated during a reaction ≡ exothermic

If heat is absorbed during a reaction ≡ endothermic

Calculating Energy of a ReactionCalculating Energy of a Reaction

H2 + Cl2 2HCl

Moles of Bonds Moles of Bonds BrokenBroken

Energy absorbed Energy absorbed (kJ)(kJ)

Moles of Bonds Moles of Bonds FormedFormed

Energy released Energy released (kJ)(kJ)

1 H-H @ 431.2 1 H-H @ 431.2 kJkJ

436436 2 H-Cl @427 kJ2 H-Cl @427 kJ 854854

1 Cl-Cl @ 1 Cl-Cl @ 243243

679679 854854

Heat of Reaction is 679 – 854 = -175kJ; energy is released during the Heat of Reaction is 679 – 854 = -175kJ; energy is released during the reactionreaction

Endothermic or exothermic?

Chemical Reactions and EnergyChemical Reactions and Energy

H2 + Cl2 Bonds are broken HCl

Energy releasedEnergy released

Calculating chemical energyCalculating chemical energy

N2 + O2 2NO

Breaking one N bond = 946 kJ/mol

Breaking one O bond = 498 kJ/mol

Forming 2 N-O bonds = 2 x 631 kJ/mol = 1262 kJ/mol

Net energy released = (946 + 498) + 2(-631) = +182 kJ/mol


Chemical Reactions and EnergyChemical Reactions and Energy

N2 + O2 Bonds are broken NO

Energy absorbedEnergy absorbed


2H2 + O2 2H2O



CH4 (g) + 2O2 (g) CO2 (g) + 2H2O (l)


Food – the ultimate potential energyFood – the ultimate potential energy

CC66HH1212OO66 + O + O22 CO CO22 + H + H22O + energyO + energy

ATP + heat

What is energy?

Do I need energy?

Where does energy

come from?

Where does the energy in food come Where does the energy in food come from?from?

COCO22 + H + H22O + energy O + energy C C66HH1212OO66 + O + O22

sun

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And Chemistry? Joules or calories. Evidence of Energy Motion Heat Light Sound