Ch. 16 Temperature & Heat and Ch. 17 Phases & Phase Changes

Ch. 16 Temperature & Heatand Ch. 17 Phases & Phase Changes

Thermodynamics • is the study of heat and thermal energy. • Thermal properties (heat and temperature) are based on the motion of individual molecules, so thermodynamics is a lot like chemistry.

Heat • Energy transferred from one body to another due to a DT between them.

Once its absorbed by the 2nd body/material it becomes internal energy.

Heat is energy in transit. • Heat flows from high to low temperatures.

Heat will flow out of the body at a higher temperature and into a body at a cooler temperature.

When the heat flows, the objects are said to be in thermal contact.

Two things can happen: • The temperature rises. • The object changes state.

Thermal Equilibrium

The state in which 2 bodies in physical contact with each other have identical temperatures. • No heat flows between them

Zeroeth Law of Thermodynamics: • If object A is in thermal equilibrium with object B, and object C is also in thermal equilibrium with object B, than objects A and C will be in thermal equilibrium if brought into thermal contact.

Temperature A measure of the average kinetic energy of the particles in a substance.

Imagine a pail of warm water and a cup of a hot water. • A 1 & 2 liter bottle of boiling water.

Temperature is NOT a measure of the total KE of molecules in the substance.

Temperature Scales 1. Fahrenheit (oF) 2. Celsius (oC) 3. Kelvin (K)

Boiling Point 1. Fahrenheit 212 oF 2. Celsius 100 oC 3. Kelvin 373 K

Freezing Point • 1. Fahrenheit 32 oF • 2. Celsius 0 oC • 3. Kelvin 273 K

Rankine Temperature Scale • Temperature scale having an absolute zero, below which temperatures do not exist, and using a degree of the same size as that used by the Fahrenheit temperature scale. • Absolute Zero corresponds to a temperature of −459.67°F;

Absolute Zero Point at which all molecular motion has stopped. We have never reached it, but are very close. Scale is used in engineering.

Temperature Difference (DT) Is the primemover or force-like quantity in a thermal system. DT – “Delta T”

Ex: 110 oF inside and 40 oF outside. What is the DT? • DT = 110 – 40 = 70 Fo

Converting Temperatures Fahrenheit to Celsius TC = 5/9(TF – 32o)

Ex: Convert 50 oF to oC TC = 5/9(TF – 32o) TC = 5/9(50 – 32o) TC = 5/9(18o) TC = 10 oC

Celsius to Fahrenheit • TF = 9/5(TC)+ 32o

Ex: Convert 20 oC to oF TF = 9/5(TC)+ 32o TF = 9/5(20)+ 32o TF = 36 + 32o TF = 68 oF

Convert Celsius to Kelvin Tk = Tc + 273.15 Tc = Tk – 273.15

Ex: Convert 72 oF to K TC = 5/9(TF – 32o) TC = 5/9(72 – 32o) TC = 22.2 oC

Thermal Expansion • With a few exceptions, all substances – solids, liquids, & gases – expand when heated and contract when cooled.

Different materials expand at rates. • The construction of structures and devices must take this into consideration.

Bimetallic Strip • Two thin strips welded together. • Usually brass and iron. • Used in thermostats.

Does a hole expand of shrink when heated?

Loosening a tight nut.

calorie • The amount of heat energy required to raise the temperature of 1 gram of water 1 oC.

1 kilocalorie (1000 calories) is used in rating food. • Written as Calorie (capital C)

Both are units of energy. • 1 calorie = 4.187 J • BTU – British Thermal Unit (English Unit)

Fuels are rated by how much heat is given off when a certain amount is burnt.

Mechanical Equivalent of Heat 1 calorie = 4.186 J Food

Conduction Process in which heat energy is transmitted from molecule to molecule of a solid. In direct contact

Conductors • A material through which heat can flow easily. ex: metals

Occurs in materials and between different materials in direct contact.

Is the result of collisions on an atomic & molecular level.

Materials that conduct heat poorly are called insulators. Ex: straw, wood, paper, cork, Styrofoam, etc.

Ch. 16 Temperature & Heat and Ch. 17 Phases & Phase Changes