Combined Gas Law

How can you combine all three laws into one equation? Boyle’s LawP x V Charles’s LawV / T Gay-Lussac’s LawP / T

Combined Gas Law relates pressure, temperature, and volume in a single statement Equation: P₁V₁ = P₂V₂ T₁ T₂

Using Combined Gas Law Lets you solve problems if more than one variable changes at a time Helps you remember all the other equations

Try Using the Combined Gas Law Find what you know and plug it in. Remember to change °C to K! P₁V₁ = P₂V₂ T₁ T₂

.58 L

Worksheet Practice of the 3 Gas Laws and Combined Gas Law

The particles that make up different gases can come in all different sizes Particles in a gas are far enough apart from each other that size has very little influence on the volume occupied by the gas

Avogadro’s principle equal volumes of gas at the same temperature and pressure contain equal numbers of particles

Avogadro’s Principle Why does this work with gases but not with liquids or solids?

Remember 1 mole = 6.02 x 10²³ Molar volume of a gas – the volume that 1 mol occupies at 0°C and 1 atm pressure

0°C and 1 atm pressure are known as… STP (Standard Temperature & Pressure)

After many experiments… 1 mol of gas at STP has a volume of 22.4 L

Using molar volume in calculations Because the volume of 1 mol of any gas at STP is 22.4 L, you can use 22.4/mol as a conversion factor when a gas is at STP. How many moles are in a sample of gas that has a volume of 3.72 L at STP?

Question? What is the volume of 4.59 mol of CO₂ gas at STP? 4.59 x 22.4 = 102.8

What is the equation for the Combined Gas Law? How do they relate to each other?

How can Avogadro’s principle fit into the equation? The volume and temp. of this tire stay the same as air is added. However, the pressure in the tire increases as the amount of air increases PV = constant nT

Experiments using known values of P, T, V, and n have determined the value of this constant Ideal Gas Constant = R The unit used for pressure determines that value

Ideal Gas Constant R = if pressure is in atm R = if pressure is in kPa R = 62.4 if pressure is in mmHg

Plugging R into the equation gives you… Ideal Gas Law – relates the number of particles to pressure, temperature, and volume

Equation: R P = V = n = R = T = Pressure Volume Moles Ideal Gas Constant Temperature

Calculations Calculate the number of moles of ammonia gas (NH₃) contained in a 3.0 L vessel at 3.00x10² K with a pressure of 1.5 atm.

Determine the Kelvin temp. required for mol of gas to fill a balloon to 1.20 L under atm pressure. Calculations

Ideal Gases vs. Real Gases Particles take up no space

Ideal Gases vs. Real Gases No intermolecular attractive forces

Ideal Gases vs. Real Gases Particles are in constant, random motion, moving in straight lines until colliding with walls or each other

Ideal Gases vs. Real Gases Follows gas laws under all conditions of temperature and pressure

All gases have volume and are subject to intermolecular interactions Collisions are not perfectly elastic However… No gas is truly ideal

Most gases will behave like ideal gases at a wide range of temperatures and pressures. Calculations can be made using gas laws that closely approximate experimental measurements

When will a real gas not follow the Ideal gas law? High Pressure Low Temperature

High Pressure Example: propane gas will liquefy if enough pressure is applied

Low Temperature Example: Nitrogen gas turns to a liquid at -196°C

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