The Gas Laws and Ideal Gases Starting on Page 418

Key Question How are the pressure, volume, and temperature of a gas related?

Gas Law 1: Boyle’s Law

Gas Law 1: Boyle’s Law Mathematical Expression: Temperature must be constant. Are pressure and volume directly or inversely proportional?

Example Problem We must be able to “move around” the equation. Let’s try it…

Gas Law 2: Charles’s Law

Gas Law 2: Charles’s Law Mathematical Expression: Pressure must be constant. Are volume and temperature directly or inversely proportional?

Example Problem We must be able to “move around” the equation.

Gas Law 3: Gay-Lussac’s Law When a gas is heated (temp increase) at constant volume, the pressure increases.

Gas Law 3: Gay-Lussac’s Law Mathematical Expression: Volume must be constant. Are pressure and temperature directly or inversely proportional?

Example Problem: We must be able to “move around the equation”.

Partner Activity Pick a partner. Work with them to create an equation that includes all three gas laws. Answer the following questions. How would you do this? What would you call it? Why would we create such an equation?

Gas Law 4: Combined Gas Law We take each mathematical expression and combined them into one equation. This way we can solve a more complex problem. Mathematical Expression: The amount of gas is constant.

Example Problem: It works the same way as he other equations, you are just given more information.

It’s easier than you think… You don’t need to memorize all four equations. Just remember the combined gas law, and you can derive the others from it when you know which variable is constant! Let’s see how it works…

Real-World Weather balloons carry data-gathering instruments high into Earth’s atmosphere. At an altitude of about 27,000 meters, the balloon bursts.

Real-World As we reach higher altitudes, the temperature decreases, causing the pressure to decrease. But the outside pressure causes the volume to increase inside the balloon to increase until it bursts. It is more affected by pressure than volume.

Real-World Solid carbon dioxide, or dry ice, doesn’t melt. It sublimes. Dry ice can exist because gases don’t obey the assumptions of kinetic theory under all conditions. You will learn how real gases differ from the ideal gases on which the gas laws are based.

Lastly, IDEAL GAS LAW What is it? There is no such thing! A gas that follows all conditions of pressure and temperature. It would have to follow kinetic theory EXACTLY. Particles could have no volume and no attraction to each other. There is no such thing! Real gases do behave like ideal gases at many conditions of temperature and pressure.

4 Variables and 1 Constant Ideal Gas Law Can be used to also calculate the amount (in moles) of a gas. Mathematical Expression: 4 Variables and 1 Constant Variables: P,V, T, and n n= amount in moles R is Constant (NEVER changes): R = 8.31(L x kPa)/(K x mol)  Must know this!

Example Problem A deep underground cavern contains 2.24 x 106 L of methane gas (CH4) at a pressure of 1.50 x 103 kPa and a temperature of 315K. How many moles of CH4 does the cavern contain?

Practice: Page 439 #’s 56, 57