1. Lorenzo Romano Amedeo Carlo Avogadro
Ch 3.2 Notes:
Dimensional Analysis and
Lorenzo Romano Amedeo Carlo Avogadro

2. Reminders about Kelvin
K = °C °C = K – 273
Absolute Zero: 0 on the Kelvin scale, has not yet been achieved and has been deemed not possible.
Fun Fact: In Celsius and Fahrenheit, absolute zero is °C and °F

3. Dimensional Analysis

4. This Not That

5. Conversion Factors
Fractions in which the numerator and denominator are EQUAL quantities expressed in different units
Example: in. = 2.54 cm
Factors: 1 in and cm
2.54 cm in.

6. Learning Check 1. Liters and mL 2. Hours and minutes
Write conversion factors that relate each of the following pairs of units:
1. Liters and mL
2. Hours and minutes
3. Meters and kilometers

7. How many minutes are in 2.5 hours?
Conversion factor
2.5 hr x min = min
1 hr
cancel
By using dimensional analysis / factor-label method, the UNITS ensure that you have the conversion right side up, and the UNITS are calculated as well as the numbers!

8. Sample Problem
You have $7.25 in your pocket in quarters. How many quarters do you have?
7.25 dollars quarters
1 dollar
= 29 quarters X

9. You Try This One!
If Jacob stands on Spencer’s shoulders, they are two and a half yards high. How many inches is that?

10. b) 244 cm c) 24.4 cm Learning Check a) 2440 cm
A rattlesnake is 2.44 m long. How long is the snake in cm?
a) cm
b) 244 cm
c) 24.4 cm

11. b) 244 cm 2.44 m x 100 cm = 244 cm 1 m Solution
A rattlesnake is 2.44 m long. How long is the snake in cm?
b) 244 cm
2.44 m x cm = 244 cm
1 m

12. Amedeo Avogadro
A well known Italian scientist who discovered that equal volumes of gases under standard temperature and pressure (STP 0°C, 1atm) is composed of 6.022x10^23 molecules.
This is known as Avogadro’s number, commonly referred to as a mol.

13. Avogadro’s Number (aka mol) 6.022x10^23 = 1 mol
NEED TO KNOW
Avogadro’s Number (aka mol)
6.022x10^23 = 1 mol
Similar to how we count dozens (12), a mol is simply another way to count 6.022x10^23.
6.022x10^23 molecules mol
1 mol x10^23 molecules

14. Let’s Practice Together
1) How many molecules in 2.5 mols?
2)How many mols are in 8.09x10^25 molecules of pure oxygen gas?
3) If there is 1 mol of a gas contains 22.4 L at standard temperature and pressure (0°C, 1atm), how many liters are in 1.5 mols at STP?

15. Let’s Practice Together
1) How many molecules in 2.5 mols?
1.5x10^24 molecules
2)How many mols are in 8.09x10^25 molecules of pure oxygen gas?
134.4 mols
3) If there is 1 mol of a gas contains 22.4 L at standard temperature and pressure (0°C, 1atm), how many liters are in 1.5 mols at STP?
33.6 L