Dimensional Analysis

• how many dollars is € 35.00 ?          (1€ =  $ 14)
          € 35 x  $ 14/  € 1 = $ 49
• what is 100 km/h in miles/hour ?    (1.6 km = 1 mi)         

               100 km/h x 1 mi/1.6km = 62.5 mi/h

• just like converting between currencies in chemistry it is usually necessary to convert between units
• this process is called dimensional analysis

STEPS:

• there are only 4 steps 

1. Identify what units you want to end up with
2. Find the conversion factors 
3. Place units in the appropriate places
4. Cancel units

EXAMPLES:

• How many miles are equal to 120 km ?

                 120 km x 1 mi/1.6 km = 75 mi  

• How many seconds are in 1.4 hours ?

              --> 1.4 h x 60 min/1 h x 60 s /1 min = 5040 s

              --> 1.4 h x 3600 s/1 h = 5040 s

• What is 50 km/h in m/s ?

                 50 km/h x 1 h/3600 s x 1000 m/1 km = 13.88 m/s = 14 m/s

• Convert 150 kJ/h into J/s :

                 150 kJ/h x 1 h/3600 s x 1000 J/1 kJ = 41.7 J/s

• Convert 230 mg/s into g/min :

                 230 mg/s x 60 s/1 min x 1 g/1000 mg = 13.8 g/min

-Eva