Introduction to Boyle’s Law By: Lisa Thompson Scrofano Audience: Secondary learners of all abilities TAKS Benchmark Chemistry Grades 10-12 Slide presentation will proceed automatically.
Learning Goal: Describe basic application of Boyle’s law Song: Under Pressure – Queen & David Bowie 1981A popular tune of Generation X What happens to pressure in a space when volume in that space increases and the temperature remains the same?
What is Boyle’s Law? This theory was discovered by Sir Robert Boyle, a 17th century scientist. The theory known as Boyle's Law states: . If the temperature remains constant, the volume of a given mass of gas is inversely proportional to the absolute pressure.
PV=kT Boyle's Law involves a relationship between three properties of a gas in a container. The volume of the container -- denoted V. Volume is measured in units of length^3 -- for example, cubic centimeters or cubic inches. The pressure of the gas -- denoted P. Pressure is measured in units of force per area -- for example, pounds per square inch. The temperature of the gas -- denoted T. Temperature is in many ways more complicated than pressure or volume. It is usually measured using one of three units -- degrees Fahrenheit, degrees Celsius, or degrees Kelvin.
PV=kT What is K? Pressure * Volume = Constant * Temperature *The value of the constant k depends on the units used for the other quantities but once the units are fixed, k is also fixed. When any one of the quantities V, P, or T is changed, one or two of the others must change so that the equation above still holds.
Before we calculate…how do we explain Boyle’s Law? Pressure is inversely proportional to the volume of the container, assuming the temperature remains the same, in other words, constant. Pressure increases when the volume goes down. Pressure decreases when the volume goes up. Let’s look at some examples of how pressure is affected by volume…
Boyle’s Law P=1/v and every day life? When you have a timed test (the “volume of time” is decreased) will your pressure increase or decrease? When the “volume” of exams increases how is your pressure?
P=1/v or pressure is inversely proportional to volume p1v1 = p2v2 helps calculate the decrease or increase of the pressure of the people in the box Imagine if each of these people were molecules and we kept squeezing the box of people smaller. What would happen?
Remember the box of people? Focus on the yellow box . The people have been replaced with molecules. What do you notice?
The Human Container We need some volunteers to be molecules in the middle of our human container. As the molecules move, we have created a large enough container for them to move easily. What happens when everyone acting as the container steps forward and cuts the volume in half? How easily do the “molecules” move?
P=1/v or PV=kT p1v1 = p2v2 Fill your mouth with air. Push the same volume of your entire mouth to one side of your cheek. What happened? Was there a change in temperature in your mouth when the air was shifted?
How to calculate the relationship between pressure and volume Look at the picture again. Suppose we have a theoretical gas confined in a jar with a piston at the top. The initial state of the gas has a volume equal to 4.0 cubic meters and the pressure is 1.0 kilopascal. With the temperature and number of moles held constant, weights are slowly added to the top of the piston to increase the pressure. When the pressure is 1.33 kilopascals the volume decreases to 3.0 cubic meters. The product of pressure and volume remains a constant (4 x 1.0 = 3 x 1.33333 ).
Boyle’s Law & Diving Boyle's Law is very important in diving. In diving, the lungs are under intense pressure, and so that drastically changes volume. If you take a breath at the surface of a body of water, it is at a pressure of about 15 psi from the atmosphere. If you dive to a depth of about 33 feet or 10 meters (slightly less for salt water), the pressure will double to 30 psi. The volume of your lungs will be halved! And if you take a full breath of compressed air at 33 ft, heading back to the surface the volume of that air will double! That's why you have to exhale on the return trip, or else your lungs would explode. Class Practice: 15psi=constant volume 30 psi = ½ volume
Don’t kill Bob the Diver! We’ve learned about Boyle’s Law and divers. Break into groups and calculate Bob’s lung pressure (psi) with each decent and accent every 10 meters. Refer to previous equation. Atmospheric pressure = 15 psi. Explain the volume. Bob will dive to 40 meters. Why should divers never pass their bubbles when coming back up? 1 10 20 30 40
Calculate 1. The volume of the lungs is measured by the volume of air inhaled or exhaled. If the volume of the lungs is 2.400 L during exhalation and the pressure is 101.70 KPa, and the pressure during inhalation is 101.01 KPa, what is the volume of the lungs during inhalation?
2. The total volume of a soda can is 415 mL. Of this 415 mL, there is 60.0 mL of headspace for the CO2 gas put in to carbonate the beverage. If a volume of 100.0 mL of gas at standard pressure is added to the can, what is the pressure in the can when it has been sealed?
3. It is hard to begin inflating a balloon. A pressure of 800.0 Kpa is required to initially inflate the balloon 225.0 mL. What is the final pressure when the balloon has reached it's capacity of 1.2 L?
2.412L 169 KPa 150 KPa
Boyle’s Law Summary– There is an inverse relationship between the volume and the pressure of an ideal gas when its temperature is held constant. As pressure decreases, volume increases. As pressure increases, volume decreases. P1 V1 = P2 V2