Charles' Law

Charles' Law says that temperature and volume vary directly. This is true at constant pressure only. The temperature for all problems using this law must be in Kelvin. The conversion for this is: C + 273.15 = K. As temperature increases, the gas gains energy. This makes it contact with the side of the container more and want to expand. The formula we use for these problems is:

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Example: Gas at 15C and 1 atm has a volume of 2.58L. What volume will it have at 38C and 1 atm?

T1=15+273.15=288.15K   V1=2.58L   T2=38+273.15=311.15K   V2=?

(2.58)(311.15)/(288.15) = 2.79L

Here are a few more practice problems like the one above!

Boyle's Law

Boyle's Law says that the relationship between pressure and volume is inverse. It deals with only two of the four variables that determine the state of a gas. The only gas that actually holds to this relationship is an ideal gas at low pressure. The equation used for this law is:

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Example: Pressure on the peak of Mt. Everest is 150mmHg. If climbers carry 10.0 L tanks with a pressure of 3.04x10^4 mmHg, what will be the volume of the oxygen when it's released?

V1=10.0L   V2=?   P1=3.04x10^4mmHg   P2=150mmHg

10(3.04x10^4) = V2(150)   =   2.0x10^3 L

Here are some more practice problems for these

Combined Gas Law

The Combined Gas Law is used to deal with changes in all of the variables: moles, temperature, pressure, and volume. The formula we use to calculate this is:

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Example: A bubble rises from the bottom of a lake when temperature and pressure are 8C and 6.4 atm. The bubble reaches the surface where it is 25C and 1atm. What's the final volume of the bubble if the initial was 2.1mL?

P1=6.4atm   V1=2.1mL   T1=8+273.15=281.15C    P2=1.00atm   V2=?   T2=25+273.15=298.15C

6.4(2.1)298.15=1(V2)281.15   =    14mL

Here are more practice problems

Avagadro's Law

Avagadro's Law says that for a gas at constant temperature and pressure, the volume is directly proportional to the number of moles of gas. Equal volumes of gases at the same temp and pressure have the same amount of particles. This relationship is even true for gases at low pressures. The relationship for this law is:

Source

Example: We have 12.2 L containing .50 moles of oxygen at a pressure of 1 atm and a temp of 25C. If all of the oxygen is converted to ozone at the same temp and pressure, what would be the volume?

3O2-->2O3

V1=12.2L    N1=.50mol    V2=?    N2=.33 mol

.5mol x 2mol/3mol = .33mol

12.2(.33)=V2(.5) = 8.13L

Calculating Heat

To calculate heat, you use the formula Q=mcAt (A is representing delta)

Q is heat in Joules
m is mass in grams
c is specific heat in J/g degrees C
At is change in temperature

Example 1: Calculate the amount of energy in joules required to heat 454 grams of water from 5.4C to 98.6C:

Q=?   m=454g    At=93.2  Ti=5.4   Tf=98.6   c=4.184
454(4.184)(98.6-5.4)= 1.77x10^5 J OR 177 kJ

Example 2: A 2.6g sample of metal requires 15.6J of energy to change its temperature from 21C to 24C. What's the identity of the metal?

m=2.6g   Q=15.6J   Ti=21   Tf=34   c=?
15.6=2.6(c)(34-21)
C=.46 J/gC OR Iron

Temperature and Heat

The Kinetic Molecular theory states that as a substance is heated, molecules gain energy. However, we cannot measure the amount of energy in the form of heat a substance contains, but we can measure the flow of heat energy. This is always from a warm to cold body until the temperature equalizes. This change is used to measure heat flow.

Exothermic: If there's an output of energy out of the system, then the system is losing energy.

Endothermic: If there's an input of energy into the system, then the system is gaining energy.

Endothermic vs. Exothermic

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Music Video Reflection

Exciting news! After submitting Hamming and I's biodiesel music video to the American Lung Association's contest, we were notified that we made it to the top 10, along with 2 other groups from our school! Now, while waiting for the official results to come out, we have the chance to earn $250 by getting the most views on our video. To help us with this, all you have to do is press on the special link below and listen to our little ukulele tune. Thanks!!

"Most Views" Link