Let’s Learn the Gas Laws

What are the 3 properties of gases? Temperature (T) Volume (V) Pressure (P) Remember, if you keep any 1 of these constant, there is a known relationship between the others

Charles Law The relationship between volume and temperature Pressure is constant

Temperature vs. Volume Graph 5 10 15 20 25 30 Volume (mL) Temperature (C) 100 – 273

Absolute Zero If a volume vs. temperature graph is plotted for gases, most lines can be extrapolated downward so that when volume is 0 the temperature is -273 C. Obviously naturally, gases don’t really reach a 0 volume, but the spaces between molecules approach 0. At this point all molecular movement stops. –273C is known as “absolute zero” (0 K) no KE- energy of motion Therefore we get the Kelvin scale…

Kelvin Scale Lord Kelvin suggested that a reasonable temperature scale should start at a true zero value. He kept the convenient units of C, but started at absolute zero. Therefore since at 0 volume, temperature is -273 C: K = C + 273. Practice: 62C = ? K From now on, we will be using Kelvin!!

Back to Charles's Law… Your data shows that… As T increases, V increases As T decreases, V decreases Therefore this is a direct relationship

But why is this important??

My experience with a hot air balloon The balloon and basket were placed in a field. The burner was ignited and a huge fan blew the heated air into the balloon on the ground. The balloon started to fill up and lift off of the ground. When the balloon was completely filled with hot air where would it be??????

Some History: Imaginative Hot Air Balloons The first balloon and one today

History behind Charles's Law In the early 1800's in France hot air balloons were extremely popular. Scientists were eager to improve the performance of their balloons. We know that no extra air was added to the balloon  so how did heating the air (gas) make it rise? One prominent French scientists, Jacques Charles, made detailed measurements on how the volume of a gas was affected by the temperature of the gas.

Jacques Charles He discovered that the volume of the gas will increase as the temperature increases Conversely he stated that a decrease in temperature results in a decrease in volume So ↑T = ↑V ↓T = ↓V In a hot air balloon, what is happening to the T? V?

A balloon and liquid nitrogen http://www.youtube.com/watch?v=al5f9q845q0 What is happening to the balloon? What is happening to the temperature? Volume?

Lets try some calculations Always set up: V1 = T1 = V2 = T2 = You will have one unknown Write down the starting temperature or volume… What is the relationship? If you want a bigger number If you want a smaller number

Joseph Louis Gay-Lussac. 1778-1850 Pressure and Temperature

Lets look at our data… Pressure Temp

Gay-Lussac’s work Determined the relationship between temperature and pressure of a gas. He measured the temperature of air at different pressures, and observed a pattern of behavior which led to his mathematical law. During his experiments volume of the system and amount of gas were held constant. He found: ↑T = ↑P ↓T = ↓P Therefore this is a direct relationship.

What is pressure? The pressure of a gas is the push exerted on the wall of the container a gas is trapped in. There are several units for pressure depending on the instrument used to measure it including: Atmosphere (atm) Millimeters of mercury (mmHg) Kilopascals (kPa) Torr (torr) We will only be using atm and torr

Why is this applicable?? Did you ever look on the back of cake mix? There are special instructions for high altitude At high altitudes, pressure is lower because there is less air above you (less push) So how will we have to adjust the temperature? Examples High Altitude (3500-6500 ft): For all pans, heat oven to 325°F.

Another example… Car tires… what happens to the pressure inside the tire during the winter (when it is cold)? As temperature decreases, pressure decreases This is why we have to add air to the tires during winter

Lets try some calculations Always set up: P1 = T1 = P2 = T2 = ** Remember temperature has to be in K and pressure in atm ** You will have one unknown Write down the starting temperature or pressure… What is the relationship? If you want a bigger number If you want a smaller number

Robert Boyle 1627 – 1631 Volume and Pressure

Lets look at our data…

Boyle’s Law Boyle’s law states that pressure and the volume of a gas are inversely proportional. At constant temperature for a fixed mass. Therefore: ↑V = ↓ P ↓V = ↑ P Therefore this is a indirect relationship.

Why is this important? Let’s try making straw snap… Hold both ends and flick it… What happened? Now reduce the volume and flick it…

Okay, but what else? Making the best water balloons… What happens if you keep filling the balloon? What is the best water balloon for a water balloon toss? Smaller – will not pop as easily What is the best water balloon to throw at someone? Larger – will pop very easily

Lets try some calculations Always set up: V1 = P1 = V2 = P2 = ** Remember pressure in atm ** You will have one unknown Write down the starting volume or pressure… What is the relationship? If you want a bigger number If you want a smaller number

S T P - Temperature = 0°C or 273K The behavior of a gas depends very strongly on the temperature and the pressure at which the gas is held. To make it easier to discuss the behavior of a gas, it is convenient to designate standard conditions, called STP. - Temperature = 0°C or 273K - Pressure = 1atm or 760mmHg or 101.3kPa