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Paperwork. HMWK deadline off by one hour Everyone get some bonus? Guest Instructors Monday – Chapter 20.1-20.3 Week After Mon & Fri That’s when the exam is ( 2 weeks) Move exam back one week, skip one lab?. Schedule Short Term. Today – Chapter 19 Next Week - PowerPoint PPT PresentationTRANSCRIPT
Paperwork
• HMWK deadline off by one hour– Everyone get some bonus?
• Guest Instructors– Monday – Chapter 20.1-20.3– Week After Mon & Fri
• That’s when the exam is ( 2 weeks)
• Move exam back one week, skip one lab?
Schedule Short Term
• Today – Chapter 19• Next Week
– Monday –Chapter 20.1-20.3 (Guest)– Tuesday – Lab #2
• Quiz#2 [Chapter 18, Labs]– Wed – Ch. 20.4-20.5– Friday – Practice Problems
• Week After– Monday – Ch. 20.6-20.7 (Guest)– Tuesday – Lab 3 & Quiz 3– Wed (Was exam) Review 17-20– Friday 21.1-21.3 (Guest)
• Then -
Chapter 19
• 1st Law of Thermo– Q=U+W (eq. 19.5)– Q = Heat– W = Work– U = Internal Energy [Any Guesses]
• Internal Energy– Sum of all KE [Thermo] – Plus Sum of all interactions [bonds]– Not U as in grav. potential energy
Signs & Such
• Q=U+W (eq. 19.5)• Talks about how heat affects a system• What does Q being + mean?
– Heat added to system• What happens if U is positive?
– Raise temperature, change state…– Chemical bonds have negative energy– Solid to liquid means U increases, less neg.
• What happens if W is positive?– System does work on its surroundings– Maybe heats up a container, etc…
Signs & Such
• Q=U+W (eq. 19.5)
• Talks about how heat affects a system
• Q+ heat enters system
• U+ Internal energy raised– Bonds broken, temperature increased
• W+ Work done on outside world
• W- Work done on system from outside
Isolated System
• Q=U+W
• System completely isolated from outside
• What is Q? (say as a function of time)
• What is W? (time dependence as well)
• Implications?
• Isolation can be attained by expansion…
Gas # molecules = n0
Temperature = T0
pressure = p0
Volume = V0
Discussion Q18.10Start
Vacuum
Gas Initial State# molecules = n0
Temperature = T0
pressure = p0
Volume = V0
Discussion Q18.10“Sudden” Hole in wall
Gas Final State# molecules = ?Temperature = ?pressure = ?Volume = ?
What Happens here?
Changes in System
• Follow equation: Q=U+W– Look at small changes
• dQ = dU + dW
• dU = dQ – dW
• dW = pdV [gaseous systems]
• dU = dQ – pdV [1st law thermo for gas]
Types of Changes
• Adiabatic (Constant Heat)
• No heat transfer to/from system
• Q = 0
• dU = dQ – dW
• dU = -dW
• As a whole: U = -W
• For a gas: dU = -pdV
Types of Changes
• Isochoric (Constant Volume)• No change in volume [Stiff container]• dV = 0• pdV = 0 = W• dU = dQ • As a whole: U = Q• For a gas: U = Q • Usually implies no work done that changes
volume• Example: Stirring liquid usually still “isochoric”
Types of Changes
• Isobaric (Constant Pressure)• No change in volume [Stiff container]• p = constant• dQ = dU + dW • dQ = dU + pdV• p is constant of integration, no V dependence• Integrate both sides Q = U + p(V)• Example: Boiling water in an open pot
Types of Changes
• Isothermal (Constant Temperature)• No change in Temp [Could add heat though…]• T = constant• dQ = dU + dW • dQ = dU + pdV• Complicated pV = nRT• p = nRT/V (Ideal Gas)• So integration not trivial even for ideal gas• Example: Icewater mixture, while both exist
Internal Energy of Ideal Gas
• Q=U+W
• dQ = dU + dW
• Gas: dW = pdV
• What does U depend on?– Reminder about U– Measure of internal KE & PE between
particles
Gas # molecules = n0
Temperature = T0
pressure = p0
Volume = V0
Discussion Q18.10Start
Vacuum
Gas Initial State# molecules = n0
Temperature = T0
pressure = p0
Volume = V0
Discussion Q18.10Final State (Again)
Q=U+W
Gas Final State# molecules = ?Temperature = ?pressure = ?Volume = ?
So what is DU?
Is there work done on gas?Is there heat input?
Internal Energy of Ideal Gas
• Q=U+W
• What does U depend on?– Temperature– Gas doesn’t change phase (or its not a gas)– Ideal Gas: No interactions between particles– No potential energy (bonding) between
particles– Diatomic molecules?
Ideal Gas Heat Capacities
• Different for different conditions• dQ = nCdT [molar heat capacity]
• Constant Pressure: CP
• Constant Volume: CV
• Constant Temperature: CT
– Wouldn’t that mean dQ = 0?
• Constant n: Cn
– n is not in C, other part of Equation
Relationship
• CP = CV + R• Derivation in text• Heat capacity larger for isobaric process
• Ratio of heat capacities• = CP/CV = 1.67 (monotomic)• = CP/CV = 1.4 (diatomic)• = CP/CV = 1.3 (“triatomic”)• Look at this closer later next week…
Reading & Assignments
• Chapter 18 assignment – Up today, Due next Friday
• Chapter 19 Assignment– Up today, Due in 1.5 weeks
• Put up practice problems– Hopefully answers, etc…
• Read chapter 19 & sect. 20.1 to 20.3 for Monday
Schedule Short Term
• Today – Chapter 19• Next Week
– Monday –Chapter 20.1-20.3 (Guest)– Tuesday – Lab #2
• Quiz#2 [Chapter 18, Labs]– Wed – Ch. 20.4-20.5– Friday – Practice Problems
• Week After– Monday – Ch. 20.6-20.7 (Guest)– Tuesday – Lab 3 & Quiz 3– Wed (Was exam) Review 17-20– Friday 21.1-21.3 (Guest)
• Then -