The Nature of Gases

Gases Occupy Space All matter, including gases, have mass and occupy space Balloon in a bottle demo The first concept of gases that we are going to explore is that gases occupy space. Gases are a form of matter and all matter have mass and occupy space. Remember that a gas can expand to fill its container, unlike a solid or liquid. Gases can also be easily compressed or squeezed into a smaller volume under pressure. So why can gases be compressed more easily than liquids or solids? Because there is more space between particles in a gas. At ordinary pressures, the distance between individual particles is of the order of ten times the diameter of the particles. At that distance, any attractions between the particles are fairly negligible at ordinary temperatures and pressures.

Balloon in a Bottle Reasoning The air/gas in the bottle is compressed. The compressed air exerts more pressure on the balloon than you can blow into it.

Kinetic Theory Tiny particles in all forms of matter are in constant motion Kinetic Theory states that all particles of matter are in constant motion, and we can confirm this with gases because we know that odors travel. The average speed of an oxygen molecule at 20C is 1700 km/h. Using this fact, we can calculate that the odor of a cheese pizza could go from DC to Mexico City in 115 min, that is if there was no other matter interrupting the oxygen molecule’s travel.

Kinetic Theory Particles in motion exert forces when they collide with other bodies Gas pressure is the result of simultaneous collision of tons of gas particles with an object Particles increase their motion with greater temperature So we know that gas particles are in constant motion, so how does that relate to the behavior of gases? Well when gas particles move about they collide with other particles and objects. If one gas particle collides with another with enough energy Explain the reason why some collisions are effective and some are ineffective. Identify the reactants and products.

https://www.youtube.com/watch?v=OkGzaSOkyf4

Balloon Demonstration Part 2 Explain the process of blowing up the balloon in terms of gas particles?

Balloon Demonstration Part 2 Gas (Carbon Dioxide) from the lungs is blown into the balloon You are increasing the number of gas particles in the balloon

Balloon Demonstration Part 3 Explain why the balloon blows up using the kinetic theory

Balloon Demonstration Part 3 The gas particles are in constant motion and exert a force or pressure on the inside wall of the balloon causing it to expand

After Mini Experiment Record your results on your notes sheet Answer the 2 analysis questions

Mini Experiment Add small drops of BTB (bromothymol blue) to the small circles in the pattern shown on the template. Be sure the drops do not touch one another. Mix 2-3 drops of each HCl and NaHSO3 in the center, large circle of the pattern. Quickly place the Petri dish over the grid to enclose the reaction (this means solid side up). Observe and record what happens in the data table for the reaction. Wipe the template with a paper towel and throw away in the garbage.

Atmospheric Pressure Air exerts pressure on Earth because gravity holds air molecules in Earth’s atmosphere Atmospheric pressure refers to the collision of air molecules with objects

The air around you exerts pressure on your body all the time. Atmospheric Pressure The air around you exerts pressure on your body all the time. As you climb a mountain, atmospheric pressure decreases https://www.youtube.com/watch?v=XctwiScoorM

Atmospheric Pressure If you have the same pressure both inside and outside (atmospheric pressure) of an object then the forces created by those objects are equal The object will not be crushed or expanded

Mauna Kea Hawaii’s tallest dormant volcano – 33,500 ft (10,200 m) from Pacific floor. World’s highest mountain island Pressure differences – crush or expand

Pop Can Demo Procedure Fill a can with 10-12 mL of water Fill a pan with cold water Heat the can until water is boiling and steam is visible Invert the can in the cold water making sure that the opening is completely submersed

The Collapsing Can What happened? When you heated the can you caused the water in it to boil. The vapor from the boiling water pushed air out of the can. When the can was filled with water vapor, you cooled it suddenly by inverting it in water. Cooling the can caused the water vapor in the can to condense, creating a partial vacuum. The extremely low pressure of the partial vacuum inside the can made it possible for the pressure of the air outside the can to crush it.

When you heated the can you caused the water in it to boil When you heated the can you caused the water in it to boil. The vapor from the boiling water pushed air out of the can. When the can was filled with water vapor, you cooled it suddenly by inverting it in water. Cooling the can caused the water vapor in the can to condense, creating a partial vacuum. The extremely low pressure of the partial vacuum inside the can made it possible for the pressure of the air outside the can to crush it.

The Collapsing Can Demonstrates: The effect of atmospheric pressure (pressure of the gases in the air) on an object The effect of temperature on a gas

Effect of Increasing Temperature on Gases Heating the water in the can Increasing the temperature of the liquid water causing the liquid to become water vapor Increasing the temperature speeds up the particles Increasing the speed means more collisions against the object Increasing the pressure inside the object

Effect of Decreasing Temperature on Gases What was the effect of putting the can in cold water? Seals the top of the can Decreasing the temperature decreases the speed of the gas particles Gas particles condense Causes a pressure difference between the atmosphere and inside the can

Standard Temperature 0ºC or 273K Celsius to Kelvin Kelvin to Celsius ºC + 273 = Kelvin Kelvin to Celsius Kelvin - 273 = ºC

Standard Pressure 101.3 kPa (kilopascals) or 1atm Convert atm to kPa x G atm 101.3 kPa 1 atm x G kPa

Pressure Continued 1 atm = 760 mmHg

Variables used to describe a gas Pressure (kPa) Volume (L) Temperature (K) n (number of moles) **Our goal is to be able to predict the behavior of a gas given specific conditions

Review Take some time to answer the practice problems in your group