1st Edition CHM 104 Lecture 25 Outline of Last Lecture I Qualitative Determination of Presence Absence of Cations in a Solution II Complex Ion Equilibria Outline of Current Lecture III IV V VI VII VIII IX Thermochemistry Energy Work Heat Types of Energy First Law of Thermodyynamics Quantifying Change Current Lecture Thermochemistry Study of Chemical Energy How it is transferred from one form to another how that energy is used to do useful work how much energy does a reaction produce Combustion and why do some reactions occur and others not Energy Something an object possesses the capacity to do work or release heat Work w Force acting over a distance if I pick up a chair and move it I have done work Heat q Flow of energy caused by a temperature difference heat flows from hot to cold As a hot cup of coffee cools it transfers energy to the air around it Heat and work are the primary ways in which energy is transferred Types of Energy Kinetic Energy associated with motion car 60 mph has kinetic energy These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute dumptruck 60 mph has more Thermal Energy associated with temperature Potential Stored Energy associated with position or combustion Chemical Form of potential energy associated with the energy in chemical bonds CH4 has stored energy released by combusting with oxygen Units for Energy Joule J Calorie cal 360 000 Joules to light a light bulb for an hour 1 cal 4 184 J Amount of energy needed to raise the temperature of 1 g H2O by 1oC 1 Cal food 1000 calories First Law of Thermodynamics ENERGY is not created or destroyed converted from one form to another or transported from one object to another We keep track of where energy is going by defining System thing being studied chemical reaction Surroundings Everything Else Energy is transferred between the system chemical reaction and surroundings everything else If system loses energy then the surroundings gain that energy and vice versa For a system the INTERNAL ENERGY E is the sum of kinetic and potential energy all types It is a STATE function STATE FUNCTION Property whose value depends on the state of the system and NOT how it got there Reaction System Initial Final Energy flows out of the system into the surroundings Quantifying change q system gains energy through heat system gives off heat w work done on system system does work If E energy flows into system energy flows out to surroundings Heat q When a system absorbs heat it s temperature increases Example How many J of heat does 10 0 g Al need to absorb to increase in temperature by 25oC Cs 0 900 J goC Work w Many types of work a chemical system can do our focus will be PRESSURE VOLUME work Work Force acting across a distance Example How much work is done if the gases in a piston cylinder expand 0 100 L against a pressure of 5 0 atm System gases