3work is done when a force is exerted over a distance. For chemists work is energy change resulting from a process.
4Types of energies:KineticPotentialRadiantThermalChemical
5Kinetic EnergyEnergy of motion (chemists’ particular ineterest)
6Potential energyAvailable by virtue (effective force) of an object’s position relative to other objects.
7Electrostatic energy is 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.
8Radiant energyComes from the sun.Earth’s primary source of energy.
9Thermal 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.
10Chemical 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.
11SI(systems integration) unit of Energy(E) Joule (J)1 kJ=1000J1cal= J
121st 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.
33Internal energy (E or U) We can’t calculate the actual numerical value of U.Instead, we can calculate ΔE or ΔU (change in internal energy).
34Internal energy (E or U) ΔU= Ufinal – UinitialUinitial : 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)
35Internal energy (E or U) (+)Ufinal > UinitialThe system has gained energy from its surroundings(-)Ufinal < UinitialThe system has lost energy to its surroundings
36Internal energy (U)ΔUsys + ΔU surr =0 (because the total energy of the universe is constant)
37Heat and work are 2 equivalent ways of changing the internal energy of a system
39U = Q (heat) + W (work) + = Change in internal energy Energy supplied to system as heatEnergy supplied to system as workU = Q (heat) W (work)
40qwUU like reserves of a bank: bank accepts deposits or withdrawals in two currencies (q & w) but stores them as common fund, U.
41Signs (+/-) will tell you if energy is entering or leaving a system + indicates energy enters a system- indicates energy leaves a system
42When q is (+) & w is (+) ΔU>0 (energy of the system increases) q(+): heat is transferred from the surroundings to the system. q (-): heat is transferred from the system to the surroundingsW (+): work is done by the surroundings on the systemW (-): work is done by the system on the surroundingsWhen q is (+) & w is (+) ΔU>0 (energy of the system increases)When q is (-) & w is (-)ΔU <0 (energy of the system decreases)
43ExcerciseCalculate 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.
45ExerciseDuring a reaction, the decrease in the internal energy of the system is 125 J and the system gains 55 J of heat.The system does the work.Volume of the system increases.W= - 70 J.Which of the statements are correct?(Esen yayinlari,2010)
47W = - PΔV 1) 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 expansionΔU= qp-wqp: heat change at constant pressure
48W = - PΔV 1) 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 compressionΔU= qp+wqp: heat change at constant pressure
49W = - PΔV2) when volume (V) of the system of a gas is constant:ΔV = o, w = oΔU = qv + wΔU = qv (the subscript “v” indicates that volume is constant)qp≠qv
50ExerciseA 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?
51solution A) ∆U= - 21kJ q= -125 kJ ∆U= q+W -21=(-125)+w w= +104kJ B) on the system.
52Referenceslibrary.tedankara.k12.tr/IB/mustafa/.../Internal%20Energy%2010A.pptEsen yayinlari, 11. sinif konu ozetli soru cozumleri, 2010.