Lessons 8, 9 and 10

Lesson 8 – It’s Sublime

In this lesson we learned about sublimation and evaporation, as well as percentage of error. Sublimation is the change of phase from a solid to a gas, such as solid CO₂ changing to a gaseous CO_2. Evaporation is the phase change from a liquid to a gas, such as water evaporating into the atmosphere. When calculating measurements for experiments and other activities, sometimes there is a percentage of error which should be known. Here is the formula to calculate the percentage as well as a few practice problems. (:

– How does the density of a gas compare with the density of a solid?

* A solid is much more dense than a gas and therefore gases have a much lesser density.

– What is the volume of 6.4 g of CO₂ (s)? (density = 1.56 g/mL)

* 1.56 = 6.4/V      6.4/1.56 = 4.1 mL

 

Lesson 9 – Air Force

In this lesson we learned about air and atmospheric pressure. Pressure is the force applied over a specific area and is measured in a force per unit. Air pressure is created from gas molecules colliding with other objects and is either be the air trapped inside a container or outside of the container. Atmospheric pressure is the pressure that is always present on earth in result of the air molecules colliding with objects on the planet. Atmospheric pressure, at sea level, is 14.7 lb/in² , referred to as one atmosphere of pressure (atm). Here are some practice problems to help. (:

– Explain what causes air pressure.

*Air pressure is caused by molecules colliding with objects or the walls of a container.

– What is the minimum pressure you need in bike tires to hold up a person who weighs 150 lbs? Assume that the tires touch the ground in a square that is 1.5 in by 1.5 in.

*Pressure = force/area      = 150 lb/ 2.25in²        = 66.67 lb/in²

 

Lesson 10 – Feeling Under Pressure

This lesson was about Boyle’s law and how to graph air pressure. I learned that gas pressure and gas volume are inversely proportional to one another because one increases while the other decreases. When graphing pressure and volume, you can use the equation: PV = k or V = k/P or P = k/V. Boyle’s Law states that the pressure of a given amount of gas is inversely proportional to its volume if the temperature and amount of gas are not changed. Here are some practice problems to help elaborate. (:

– How is the relationship between gas pressure and gas volume different from the relationship between gas volume and gas temperature?

* As gas pressure decreases, the volume of the gas increases, which is the opposite effect of when gas temperature increases because the volume would then also increase.

– Describe how pressure varies as the volume of a trapped gas changes.

* The pressure would increase as the volume decreased and vice versa.

 

 

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