Unit Conversions Using Dimensional Analysis We call this

“Picket Fence” Is a method to convert units. Examples include: Feet Inches Kilometers Meters

Why is Dimensional Analysis Important • Units are constantly needing to be converted throughout

Principle Behind Dimensional Analysis • You can multiply anything by 1 without changing the

How Do We Multiply By 1 If the same thing is on the top

All Equalities = 1 Any time you put two things that are equal to

All Equalities = 1 It doesn’t matter which is on top and which is

1 km = 1000 m (A metric equality) Any equality can be written two

The Rules 1. Write down “given” + unit 2. Draw a horizontal & vertical

For example: Convert 25 km to meters Use the conversion factor that allows units

For example: Convert 25 km to meters (m) Use the conversion factor that allows

Example: Convert 12. 5 g to kg (1) (4) 12. 5 g (3) 1

• Here’s a lady that talks really fast explaining dimensional analysis. – Dimensional

Try: How many centimeters are there in 5. 54 inches?

Slides: 16

Download presentation

Unit Conversions “Using Dimensional Analysis” We call this the “Picket Fence” method to convert units (the book calls it the Factor-Label method to convert from one unit to another. (pg. 130 -134 in text) Units are our friends, really!

“Picket Fence” Is a method to convert units. Examples include: Feet Inches Kilometers Meters Kilograms Grams

Why is Dimensional Analysis Important • Units are constantly needing to be converted throughout chemistry. • Stoichiometry (the relationship between quantities of reactants and products in a chemical reaction) problems depend on it.

Principle Behind Dimensional Analysis • You can multiply anything by 1 without changing the physical meaning.

How Do We Multiply By 1 If the same thing is on the top and the bottom of a fraction, = 1 Then they cancel out… and become 1

All Equalities = 1 Any time you put two things that are equal to each other 1000 g = 1 kg On top and on bottom 1000 g ----- = 1 1 kg Then they cancel out… and become 1.

All Equalities = 1 It doesn’t matter which is on top and which is on bottom. 1000 g ----- = 1 1 kg or 1 kg ----- = 1 1000 g Both cancel out… and become 1.

1 km = 1000 m (A metric equality) Any equality can be written two ways (conversion factors) 1000 m = 1 km = 1 1 km 1000 m Which one to use? Depends on which direction you are trying to go.

The Rules 1. Write down “given” + unit 2. Draw a horizontal & vertical line “picket fence” 3. Write “wanted” / “given” on the fence 4. Enter proper #s for “wanted units & “given” units 5. Cancel units & do the math

For example: Convert 25 km to meters Use the conversion factor that allows units to cancel. 1000 m or 1 km picket fence 1 km 1000 m “given” unit = “want” unit

For example: Convert 25 km to meters (m) Use the conversion factor that allows units to cancel. Just a little Scientific 1000 m notation picket fence 1 km 25 km “given” 1000 m = 25000 m (or 2. 5 x 104 m) 1 km conversion factor ‘want’

Example: Convert 12. 5 g to kg (1) (4) 12. 5 g (3) 1 kg 1000 g (2) = 0. 0125 (5) Don’t forget the units kg

See what happens without UNITS? !? !?

• Here’s a lady that talks really fast explaining dimensional analysis. – Dimensional Analysis Video Demostration

Try: 18. 2 km to m

Try: How many centimeters are there in 5. 54 inches?