# Question #7af06

##### 1 Answer

#### Explanation:

You are right, this is a job for the **ideal gas law** equation, which as you know looks like this

#color(blue)(|bar(ul(color(white)(a/a)PV = nRTcolor(white)(a/a)|)))" "# , where

*universal gas constant*, usually given as

**absolute temperature** of the gas

Now, every time you're dealing with problems that involve the ideal gas equation, your focus should be on making sure that the **units** given to you **match those** used in the expression of the universal gas constant,

In this particular case, you must convert the volume from *milliliters* to *liters* and the temperature from *degrees Celsius* to *Kelvin* by using the conversion factors

#color(purple)(|bar(ul(color(white)(a/a)color(black)("1 L" = 10^3"mL")color(white)(a/a)|))) " "# and#" "color(purple)(|bar(ul(color(white)(a/a)color(black)(T["K"] = t[""^@"C"] + 273.15)color(white)(a/a)|)))#

So, the problem provides you with

What you need to do now is isolate

#(P * color(red)(cancel(color(black)(V))))/color(red)(cancel(color(black)(V))) = (nRT)/V#

#P = (nRT)/V#

Now plug in your values to get the value of

#P = (0.255color(red)(cancel(color(black)("moles"))) * 0.0821("atm" * color(red)(cancel(color(black)("L"))))/(color(red)(cancel(color(black)("mol"))) * color(red)(cancel(color(black)("K")))) * (273.15 + 28)color(red)(cancel(color(black)("K"))))/(748 * 10^(-3)color(red)(cancel(color(black)("L"))))#

#P = "8.429 atm"#

Rounded to two **sig figs**, the number of sig figs you have for the temperature of the gas, the answer will be

#P = color(green)(|bar(ul(color(white)(a/a)"8.4 atm"color(white)(a/a)|)))#

So, as a conclusion, always **check the units first** to make sure that they match those used for

Once you're certain that the units match, isolate whichever variable you must determine on one side of the equation and plug in your values.

As a side note, Dalton's Law of Partial Pressure is applicable for **gaseous mixtures**, i.e. when you have two or more gases in the same volume.