Thermodynamics

RAT 11

Class Objectives Be able to define: thermodynamics temperature, pressure, density, equilibrium, amount of substance states of matter and define them in the context of a phase diagram gas laws

Thermodynamics Thermodynamics: “Therme” meaning heat, and “Dynamics” meaning strength Thermodynamics is the science of what is possible and impossible Major limitation: Cannot predict how long the process takes (This is the subject of rate processes)

Thermodynamic Properties Temperature = “degree of hotness” Rapidly moving molecules (atoms) have a high temperature Slowly moving molecules (atoms) have a low temperature High T Low T

Thermodynamic Properties Pressure - force per unit area F A Weight Impact change impact and weight to something cool like bevo...

Thermodynamic Properties Density - mass per unit volume High density Low density fill boxes

Thermodynamic Properties Amount of Substance – how much is there 1 2 3 12 144 6.022 × 1023 … ………. ………………... Dozen Gross Avogadro’s Number

Pair Exercise 1 A cube of osmium measures 0.2 m on a side. It sits on a table. At the contact between the table and osmium, calculate the pressure (N/m2). Note: Densities may be found in Table 11.1 Foundations of Engineering

States of Matter Solid Liquid Gas Plasma

Pressure, Temperature, and State Plasma Gas Vapor Liquid Solid Ttriple Tcritical Ptriple Pcritical Pressure Temperature Critical Point Triple

Gas Laws apply only to perfect (ideal) gases Boyle’s Law Charles’ Law Gay-Lussac’s Law Mole Proportionality Law

Boyle’s Law T = const n = const P1 V1 P2 V2

Charles’ Law T1 V1 T2 V2 P = const n = const

Gay-Lussac’s Law T1 P1 T2 P2 V = const n = const

Mole Proportionality Law T = const P = const n1 V1 n2 V2

Perfect Gas Law The physical observations described by the gas laws are summarized by the perfect gas law (a.k.a. ideal gas law) PV = nRT P = absolute pressure V = volume n = number of moles R = universal gas constant T = absolute temperature

Values for R

Pair Exercise 2 A balloon is filled with air to a pressure of 1.1 atm. The filled balloon has a diameter of 0.3 m. A diver takes the balloon underwater to a depth where the pressure in the balloon is 2.3 atm. If the temperature of the balloon does not change, what is the new diameter of the balloon?

Energy Energy is the capacity to do work, but work is a form of energy... It is easier to think of energy as a scientific and engineering “unit of exchange”, much like money is a unit of exchange. Example 1 car = $20k 1 house = $100k 5 cars = 1 house =

Energy Equivalents A case for nuclear power? 1 kg coal = 42,000,000 joules 1 kg uranium = 82,000,000,000,000 joules (82x1012) 1 kg uranium = 2,000,000 kg coal!!

Heat Heat is the energy flow resulting from a temperature difference. NOTE: HEAT AND TEMPERATURE ARE NOT THE SAME!

Example Temperature Profile in Rod Heat T = 100oC T = 0oC Vibrating copper atom Copper rod

Work Heat flows due to a temperature “driving force” Work is the energy flow from any other driving force

Types of Work Work Driving Force Mechanical Force (Physical) Shaft work Torque Hydraulic Pressure Electric Voltage Chemical Concentration

Mechanical Work F F D x

Mechanical Work i.e., work is the area under the F vs. x curve (assume F is not a function of x) i.e., work is the area under the F vs. x curve

PV Work (Hydraulic) Dx P F A DV P = const

Pair Exercise 3 An ideal gas is contained in a closed system. Under constant pressure, the container is compressed from V1 to V2 (volume). Derive the equation for work in terms of the universal gas constant and temperature.