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Thermochem%20%2804_01_08%29

# Thermochem%20%2804_01_08%29 - First Law Thermochemistry 1...

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1 1 First Law: Thermochemistry Chapter 6: First Law 6-2 Thermodynamics: First Law Energy flow is key in science; understanding it will help us to understand WHY things occur. Thermodynamics was developed independent of theory through observation of bulk matter Thermodynamics : Study and measure of the nature of heat and energy and its transformations To deal with large groups of molecules and atoms we need to define THREE parameters: System, Surroundings and Thermodynamic Universe

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2 Chapter 6: First Law 6-3 Thermodynamics: First Law System : the part of the universe of immediate interest; can be closed , open or isolated; Surroundings : the portion of the universe that can exchange energy and matter with the system; Thermodynamic Universe : System + Surroundings System Surroundings E in : + E out : - Open System : Exchanges both E and matter with Surroundings; Closed System : Exchanges only E with Surroundings; Isolated System : Exchanges NEITHER with Surroundings Sign is from the point of view of the System Chapter 6: First Law 6-4 An Auto A Battery A perfect Thermos
3 Chapter 6: First Law 6-5 Work ( w ) Motion against an opposing force; a directed motion thru a distance; w = F Δ x Capacity of a system to do work is called Internal Energy (U) Most important: Δ U = U final U initial If E transfer is only due to work then Δ U = w Work is either expansion or nonexpansion ( Δ V 0 vs. Δ V= 0) w = P ext Δ V (since w = – when system does work) Chapter 6: First Law 6-6

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4 Chapter 6: First Law 6-7 Work If P ext does change in infinitesimally small amts, then process is REVERSIBLE : a process in which an infinitesimally small change in the opposite direction will cause the process to reverse direction w = P ext Δ V ( P ext must be constant) Work is in L-atm: 1 L-atm = 101.325 J If is P ext = 0, then free expansion occurs 298 K 305 K 298 K 298 K Chapter 6: First Law 6-8 Process Lingo-1 Extensive Properties : a property of a system dependent on how much material or how big a system you have. Intensive Properties : a property of a system that is NOT dependent on how much material or how big a system you have. Thermodynamic State : a condition of a system in which constraints have been enforced. Thermodynamic Process : process leading to a change in the thermodynamic state of a system (physical or chemical). Equilibrium : the state achieved by a system when ALL properties cease to change with time.
5 Chapter 6: First Law 6-9 Process Lingo-2 Isothermal : No Δ T Isobaric : No Δ P Isochoric : No Δ V Adiabatic : a process in which no loss of energy as heat is seen (No Δ q ); Chapter 6: First Law 6-10 Reversible Work dw = PdV ( since P int = P ext ) Since P is a function of V: dw = !

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Thermochem%20%2804_01_08%29 - First Law Thermochemistry 1...

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