In this lesson our instructor talks about change due to heat. First, he discusses linear expansion, volume expansion, gas expansions, the mole, and the ideal gas law. Then he talks about water, change of phase and heat of transformation. Four complete example problems round up this lesson.
As an object's temperature rises, its dimensions will begin to increase. Different materials have different coefficients of linear expansion (α). The change in length is given by
∆L = L α(∆T).
Similarly, the volume will also increase as the temperature rises. The coefficient of volume expansion is β = 3α.
∆V = V β(∆T).
The above two formulas do not work for gases. They work fine for solids and liquids, but because gases already expand to fill their container, we need a different equation. And for that, we need-
-The Mole (mol) is a measure of how many atoms/molecules/objects there are in a substance. If m is the molecular mass of the substance and M is the mass of the substance in grams, then n=[M/m] is the number of moles.
In a mole there are NA = 6.022 ·1023 [objects/mol]. This is called Avogadro's number.
We can model the behavior of a gas with the Ideal Gas Law:
pV = nRT.
p is the pressure of the gas. [Note: absolute, not gauge pressure].
V is the volume of the gas.
n is the number of moles of gas.
R is the gas constant: R = 8.314 [J/(mol·K)].
T is the temperature (in kelvin) of the gas.
As more and more thermal energy is added to a substance, it will change phase: first from solid to liquid, then from liquid to gas. If thermal energy is removed, it will do the reverse. The specific change over temperatures vary depending on pressure.
It takes thermal energy to change phase. The amount of heat depends on the substance and the mass of the object:
Q = Lm,
where L is a proportionality constant that varies depending on substance and phase type. This heat is put into the substance if it is going to a higher energy phase, and removed if going to a lower energy phase.
Change Due to Heat
Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.
This book includes a set of features such as Analyzing-Multiple-Concept Problems, Check Your Understanding, Concepts & Calculations, and Concepts at a Glance. This helps the reader to first identify the physics concepts, then associate the appropriate mathematical equations, and finally to work out an algebraic solution.