Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work...

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Transcript of Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work...

Page 1: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.
Page 2: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

EnergyCapacity to do work

Page 3: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

workis done when a force is exerted over a distance.

For chemists work is energy change resulting from a process.

Page 4: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Types of energies:KineticPotential Radiant ThermalChemical

Page 5: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Kinetic EnergyEnergy of motion (chemists’ particular ineterest)

Page 6: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Potential energyAvailable by virtue (effective force) of an object’s position relative to other objects.

Page 7: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Electrostatic energyis one of the most important forms of PE.

It arises from the interactions between charged particles.

It is directly proportional w/ the charges of 2 interacting particles & inversely proportional to the distance separating the 2 particles.

Page 8: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Radiant energy

Comes from the sun.Earth’s primary source of energy.

Page 9: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Thermal energyEnergy associated w/ the random motion of atoms & molecules.

Thermal energy≠ temperature, but it’s dependent on the temp.

The more vigorous the motion of the atoms&molecules in a sample of matter, the hotter the sample is & the greater its thermal energy.

Page 10: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Chemical energyis the potential energy stored in the arrangements of the atoms of the substances.

When a substance participates in a chemical rxn, the chemical energy is gained, lost, or converted into another type of energy.

Page 11: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

SI(systems integration) unit of Energy(E)Joule (J)

1 kJ=1000J1cal= 4.186 J

Page 12: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

1st LAW OF THERMODYNAMICS: THE LAW OF CONSERVATION OF ENERGY

Energy is conserved!!!Energy can neither be created nor destroyed.

When one form of energy disappears, another form of energy w/ equal magnitude appears.

Page 13: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

All forms of energy are interconvertible!!!

Page 14: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

ENERGY CHANGES IN CHEMICAL REACTIONSAlmost all chemical reactions absorb or release energy, generally in the form of

HEAT

Page 15: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Heat (Q) Is the transfer of thermal energy between two bodies that are at different temperatures.

Heat flowFrom hot object ---- cold object

Page 16: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Thermochemistry Is the study of heat changes in chemical rxns.

Page 17: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

systemThe specific part of the universe that’s of interest to us.

Surroundings:Includes everything else in the universe.

Page 18: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

The chemicals usually constitute the system &the container and everything beyond them (including us) are considered

surroundings.

Page 19: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Types of systemsOpen ClosedIsolatedIsothermalIsochoricisobaric

Page 20: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Types of systems1) open system

Page 21: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Types of systems2) closed system

Page 22: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Types of systems3) isolated system

Page 23: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.
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Page 25: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Volume of the closed system remains constant (ΔV= 0)

Types of systems4) isochoric (isovolumetric)system

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Pressure stays constant (ΔP=0)

Types of systems5) isobaric system

Page 27: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Temperature remains constant (ΔT=0)

Types of systems6) isothermal system

Page 28: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Energy in the form of heat can be transferred from the system to the surroundings, or from the surroundings to the system.

Page 29: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

energyMore specifically is,

The capacity to do work or

to transfer heat.

Page 30: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Internal energy (E or U)Internal energy of the system is the sum of all kinetic and potential energies of all the “particles” in the system.

Page 31: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Internal energy (E or U)

For the system of frozen ice or still water, internal energy includes motion of H2O molecules, their rotations and vibrations, energies of the nuclei and electrons.

Page 32: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Internal energy (E or U)

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We can’t calculate the actual numerical value of U.

Instead, we can calculate ΔE or ΔU (change in internal energy).

Internal energy (E or U)

Page 34: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

ΔU= Ufinal – Uinitial

Uinitial : Internal energy of the system at the beginning( refers to the reactants in a chemical rxn)

Ufinal : Internal energy of the system after the change( refers to the products in a chemical rxn)

Internal energy (E or U)

Page 35: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

ΔU (+)

Ufinal > Uinitial The system has gained energy from its surroundings

(-)

Ufinal < Uinitial The system has lost energy to its surroundings

Internal energy (E or U)

Page 36: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

ΔUsys + ΔU surr =0 (because the total energy of the universe is constant)

Internal energy (U)

Page 37: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Heat and work are 2 equivalent ways of changing the internal energy of a system

Page 38: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

RELATING ΔU TO HEAT AND WORK

Page 39: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

+=Change in internal energy

Energy supplied to system as heat

Energy supplied to system as work

U = Q (heat) + W (work)

Page 40: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

q

w

q

wU

U like reserves of a bank: bank accepts deposits or withdrawals in two currencies (q & w) but stores them as common fund, U.

Page 41: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Signs (+/-) will tell you if energy is entering or leaving a system

+ indicates energy enters a system

- indicates energy leaves a system

Page 42: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

q(+): heat is transferred from the surroundings to the system.q (-): heat is transferred from the system to the surroundings

When q is (+) & w is (+) ΔU>0 (energy of the system increases)

When q is (-) & w is (-)

ΔU <0 (energy of the system decreases)

W (+): work is done by the surroundings on the system

W (-): work is done by the system on the surroundings

Page 43: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

ExcerciseCalculate ΔU for a system undergoing an

endothermic process in which 15.6 kJ of heat flows & where 1.4 kJ of work is done on the system.

Page 44: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

solutionQ= +15.6kJW= +1.4kJ∆U= (+15.6kJ) + (+1.4kJ)= 17.0kJ

Page 45: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

ExerciseDuring a reaction, the decrease in the

internal energy of the system is 125 J and the system gains 55 J of heat.

I.The system does the work.II.Volume of the system increases.III.W= - 70 J.

Which of the statements are correct?(Esen yayinlari,2010)

Page 46: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

answer:I and II

Page 47: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

W = - PΔV1) when pressure (P) of the system of a gas is constant :

a) ΔV might increase because of expansion of the gas.

- w (-), since work is done by the system through expansion

ΔU= qp-w qp: heat change at constant pressure

Page 48: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

W = - PΔV1) when pressure (P) of the system of a gas is constant:

b) ΔV might decrease because of compression of the gas.

- w (+), since work is done on the system through compression

ΔU= qp+w

qp: heat change at constant pressure

Page 49: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

ΔV = o, w = o

ΔU = qv + wΔU = qv (the subscript “v” indicates that volume is constant)

qp≠qv

W = - PΔV2) when volume (V) of the system of a gas is constant:

Page 50: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

ExerciseA system loses 21 kJ of its internal energy when it releases 125 kJ of heat.

A) calculate the work associated w/ this process?

B) is the work done on or by the system?

Page 51: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

solutionA) ∆U= - 21kJ q= -125 kJ

∆U= q+W -21=(-125)+w w= +104kJ

B) on the system.

Page 52: Energy Capacity to do work work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.

Referenceswww.erlanger.k12.ky.us/teachers/Gels.../che

mical%20reactions.pptlibrary.tedankara.k12.tr/IB/mustafa/.../

Internal%20Energy%2010A.ppthttp://www.goalfinder.com/product.asp?prod

uctid=102Esen yayinlari, 11. sinif konu ozetli soru

cozumleri, 2010.


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