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Chapter 10Thermodynamicssection 1What is Energy?energy (def)-the capacity of an object to do work or produce heatCh. 10 is concerned with 2 types of energy: kinetic and potential

potentialkinetickinetic energy (def)-energy due to the motion of an objectis a measure of how fast something is movingdepends on the mass of an object and its velocitycan be calculated by:KE = mv2KE is kinetic energym is mass v is velocity

potential energy (def)- energy due to the position or composition of an objectis a measure of stored energypositional example: water held behind a dam

potential energy (cont.)compositional example: the energy stored in unburned gasolinehere the potential energy is stored as chemical energy within the atomsduring combustion this energy is released as bonds are broken and new bonds are made

gasoline + oxygen carbon dioxide + water + energy

(gravitational) potential energy can be converted to kinetic energyexample: a falling ball---initial position:at first, the ball has high potential energy (due to gravity) because its height is highit has low kinetic energy because it is not moving

example: a falling ball---as it falls:the potential energy decreases as its height (distance from the ground) decreasesthe kinetic energy increases as the velocity picks up

example: before-during-after:at any time during the fall the total energy remains the same

Etotal = EKE + Epot

(as the potential energy decreases the kinetic energy of the falling ball increases)

Etotal = EKE + Epot

All Energy is Measured in Joulesenergy can take many forms; all can be measured in joules (J)energy transfers are also measured in joulesthe amount of energy transferred from one sample must be equal to the energy received by a second sample

James Joule1818-1899The amount of energy transferred from one sample must be equal to the energy received by a second samplethe total combined energy of the 2 samples remains constantenergy is not created or destroyed in a transfer

Law of Conservation of Energy (1st Law of Thermodynamics)law of conservation of energy (def)- energy cant be created or destroyed, but it can be converted from one form to another

the total amount of energy in the universe is constant

Temperature and Heat are not the Same Thingtemperature (def)-a measure of the average kinetic energy of an objectthe temperature of a sample depends on the average kinetic energy of its particlesthe higher the temperature, the faster the particles are moving

temperature is an intensive propertyintensive property (def)-a property that does not depend on the amount (# of particles) of a sampleexample: a small cup of 96C water is at the same temperature as a huge Cauldron of 96C of water (the particles in each have the same average speed)

Heatheat (def)-the energy transferred between objects that are at different temperaturesheat is always transferred from the warmer object to the cooler objectthe study of heat is called thermodynamicsheat is an extensive property

Heat is an extensive propertyextensive property (def)-a property that depends on the amount of the samplethe amount of energy that can be transferred as heat depends on the amount of the sampleexample: there is more heat in a cauldron of 96C water than in one cup of 96C waterif two samples of the same substance are at the same temperature, the larger sample can transfer more heat because it has more particles

Describing Energy Changesto study the energy changes during a process you must first determine the system and surroundingsthe system is what you are studying, it is the part of the universe you are focusing attention onthe surroundings are everything else; everything outside the system

Describing Energy Changes (cont.)the change in energy (E) for a process is equal to the difference between the energy of the system after the process and before the processE = Efinal - Einitial

Exothermic vs. Endothermicexothermic processin an exothermic process heat exits the system and is released into the surroundingsan exothermic process or reaction will feel hot

exothermic process (cont)the change in energy for an exothermic process is negativethe final energy of the system is less than the initial energy of the system because heat is releasedE is negative; Efinal 0E = Efinal - Einitial(where Efinal Einitial )

Exothermic vs. Endothermic (cont.)endothermic processin an endothermic process or reaction heat enters the system as it absorbs heat from the surroundingsan endothermic process will feel cold

endothermic process (cont)the final energy of the system is more than the initial energy of the system because heat is gained

E is positive; Efinal 0E = Efinal - Einitial(where Efinal Einitial )

Calorie vs. Jouleenergy can be measured in calories (cal) or joules (J)calorie (def)-the amount of energy (heat) required to raise the temperature of one gram of water by one degree Celsiusconversions:1 calorie = 4.184 joules1 cal = 4.184 J

calorie (cal) vs. Calorie (Cal)

food energy is often measured in Calories (Cal)

1 Calorie (food) = 1 kilocalorie 1 Cal = 1000 cal

Specific Heatdifferent substances respond differently to being heatedspecific heat (def)-the amount of energy needed to raise the temperature of one gram of a substance by 1Cthe unit for specific heat is J/gC (joule per gram degree Celsius)the symbol for specific heat is cp

Specific Heat (cont.)a high specific heat means a substance can absorb a lot of energy before its temperature is raisedwater has a high specific heatmetals have low specific heats

Heat Calculationsheat changes are calculated differently depending on whether the substance remains in state during the changewhen the substance remains IN STATE, only a temperature change occurs ( the substance does not change state)

when a substance remains in state Q (heat) is calculated using this formula:Q = m Tcp(Q means heat, m means mass, cp means specific heat and T means the change in temperature) .orQ = mass x T x specific heat (T = Tfinal Tinitial)if Q is positive the process is endothermic (heat was absorbed)if Q is negative the process is exothermic (heat was released)

during a phase change (change of state) a different formula is needed:Q = mass x heat of fusion (or heat of vaporization)

Molar Heat Capacitymolar heat capacity (def)-the energy (heat) needed to increase the temperature of 1 mole of a pure substance by 1 Kthe symbol C stands for molar heat capacitythe unit for molar heat capacity is J/mol K (joule per mol Kelvin)molar heat capacity can be calculated using the following:q = n C Theat = (amt. in mol)(mol. heat cap.)(change in temp.)the equation shows the amount of heat (q) needed to increase the temperature of n moles of a substance by T

Read p. 343-344. List at least 2 important facts for each heading.K. Molar Heat Capacity Depends on the Number of AtomsL. Molar Heat Capacity is Related to Specific HeatM. Heat Results in Disorderly Particle Motion