# How do you convert #"255 mm Hg"# to #"atm"#? What about #"620 torr"# to #"PSI"#?

##### 1 Answer

**THE CONVERSION RATIOS**

There is a **conversion factor** for going from

#\mathbf("1 atm" = "760 mm Hg" = "760 torr")#

There also exists a conversion factor for

Turns out it's

#\mathbf("51.7149 torr = 1 PSI")# .

(Google is a great resource. You should practice with it!)

**PERFORMING THE CONVERSIONS**

**(1)**

Let's start from the equality we just wrote out.

#"1 atm"# #=# #"760 mm Hg"#

What happens if we divide by

#(1 cancel"atm")/(1 cancel"atm")# #= 1# #= "760 mm Hg"/"1 atm" = "1 atm"/"760 mm Hg"#

This implies that multiplying by this ratio does NOT change the validity of your answer... only the units. (It preserves your numerical information.)

Thus, we get:

#color(blue)(P_"atm") = 255 cancel"mm Hg" xx "1 atm"/(760 cancel"mm Hg")#

#=# #color(blue)("0.336 atm")#

So now you have the **same** *pressure* in **different** *units*.

**(2)**

Like before, we have a ratio that is equal to

#1 = "51.7149 torr"/"1 PSI" = "1 PSI"/"51.7149 torr"#

This ratio is used as follows:

#color(blue)(P_"torr") = 620 cancel"torr" xx "1 PSI"/(51.7149 cancel"torr")#

#=# #color(blue)("12.0 PSI")#

Again, the **same** *pressure* as **different** *units*.