Important Definitions for Gas Laws Unit
Temperature Measure of the average kinetic energy of the particles in a substance What is kinetic energy? Heat - the transfer of energy from one substance to another due to temperature differences Goes from _____________energy to _____________ energy
Volume The amount of space occupied by a sample or substance
Pressure Force divided by area A “push” what we will use
What is a gas? Gas – no definite shape or volume It will take shape of container it is contained in Gases have 3 properties we can measure: Temperature Volume Pressure
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
Three Gas Laws Charles Law Gay-Lussac’s Law Boyles Law
Volume and Temperature Charles Law Volume and Temperature
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. –273C 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: 62C = ? 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??????
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?
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 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. Pressure and Temperature
Lets look at \data… Pressure Temp
Gay-Lussac’s work Determined the relationship between temperature and pressure of a gas. 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.
REVIEW: 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) You need to be able to convert between any of these if you are given the conversion factors…
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 Volume and Pressure
Lets look at 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