Chapter 10 Thermal Energy

Chapter Objectives Define Temperature Converting between the 3 temperature scales Identify Linear Expansion Utilize the Coefficient of Linear Expansion Compare Linear, Area, and Volumetric Expansion Apply the Kinetic Theory of Gases

Temperature Heat is defined as the energy exchanged between objects. Temperature is the measurement of the average kinetic energy of an object.

Thermal Equilibrium Two objects in thermal equilibrium with each other are at the same temperature.

Temperature Scales Fahrenheit is the scale used in the United States –Freezing point of water 32 o –Boiling point of water 212 o Celsius is the most common used scale around the world –Often thought of as a member of the metric system Kelvin scale is the most common used scale in the world of science –Along with the Celsius scale, these are the SI accepted measurements

Celsius Scale The Celsius scale is set up based on the critical points of water –Freezing point 0 o –Boiling point 100 o Positive and negative values exist on the Celsius scale

Kelvin Scale The Kelvin scale is defined as 1/ of the temperature of the triple point of water. –There is no negative values on the Kelvin scale. –The lowest point is often called absolute zero. Freezing point of water – Boiling point of water – For most calculations in this class, temperature should be in Kelvin.

Triple Point The triple point of water is the point at which conditions allow for all three phases of water to exist in equilibrium. Those conditions describe a single, specific pressure and temperature. –0.01 o C –4.58 mm Hg atm

Finding Freezing and Boiling Points Boiling points and Freezing points can change as environmental conditions change –Standard critical points are measured at accepted atmospheric pressure As pressure goes up, –Boiling point goes up –Freezing point goes up As pressure goes down, –Boiling point goes down –Freezing point goes down

Converting Between Scales To convert between the Fahrenheit and Celsius scales, To convert between Celsius and Kelvin scales, T F = 9 / 5 T C + 32T = T C

Linear Expansion Much like the behavior of gases, solids and liquids expand. Each material expands at different rates based on their chemical make-up. Due to this, a constant must be used for each material called the average coefficient of linear expansion.  L =  L 0  T Notice this calculates the change in length, not the final length.

Area and Volumetric Expansion If the linear dimension expands, then the area dimension must expand as well. For this, there is an average coefficient of area expansion. And also an average of volumetric expansion.  A =  A 0  T  V =  V 0  T

Kinetic Theory of Gases 1)The number of molecules are large, but the space between them is large compared with the volume. 2)The molecules move randomly in any direction. 3)All collisions of the molecules are perfectly elastic. 4)The forces between molecules are negligible. 5)The gas is a pure substance. Meaning all molecules are identical.

Ideal Gas Law The ideal gas law varies slightly for physics versus chemistry. That is due to Boltzmann’s Constant (k B ). k B = 1.38 x J / K Chemistry’s version uses the ideal gas constant (R). R = 8.31 J / (mol *K) PV = N k B T PV = nRT P is pressure (N/m 2 ) V is volume (m 3 ) T is temperature (K) N is number of particles n is number of moles

3 rd Version of Ideal Gas Law Assuming the amount of gas (N 1 = N 2 ) remains constant in a closed container, we can derive a 3 rd version of the ideal gas law. This version will also help us to see the basis for the 3 gas laws from chemistry (Boyle’s Law, Charles’ Law, and Gay- Lussac’s Law). Leaving us with T1T1 P1V1P1V1 T2T2 P2V2P2V2 =