As you approach the gas laws perform the following problems...

As you approach the Gas laws, perform the following problems using the equation PV = nRT provided in the presentation. Remember that n (number of moles) can be further derived as n = g / MW (molecular weight). Then solve the 2 problems below. The final answer should be rounded off to 2 decimal places (e.g. 2.678 L rounded off to 2.68 L). Use the gas constant R = 0.08205 L-atm/mole-K. 1. What is the volume in liters (L) of 2 moles of an ideal gas at 25°C and 790 mmHg? (Remember that temperature must be expressed first in Kelvin) 2. Assuming that a 1.5 g gas occupying a volume of 500 mL at a pressure of 2.5 atm and a temperature of 75°C is behaving like an ideal gas. What is the molecular weight (in g/mol) of the gas?

Transcript

00:02 For part a, we have to use the ideal gas law to find the volume in liters of a gas that we have two moles of at 25 degrees celsius, so that's our temperature, and a pressure of 790 millimeters of mercury.

00:22 So the first thing we're going to do is we're going to change our temperature to kelvin, so that's going to be 298 kelvin, and now we're going to change that 790 millimeters of mercury, we're going to change that to atmospheres, so that's going to be over 760 millimeters of mercury.

00:49 So when we divide 790 by 760, we get 1 .03947 atmospheres.

01:04 Now why am i converting to kelvin and atmospheres? well it's because i want to use the gas constant, or the r value, of 0 .08206, and this has units of liters atmospheres over mole kelvin.

01:25 So we're looking for volume, so let's rearrange our pivner equation.

01:30 That's going to be v is equal to nrt all over p.

01:37 So now let's put in our values.

01:39 We have 2 times 0 .08206 times 298.

01:50 All of this is going to be over 1 .03947, and when we do this fun math, we come up with 47 .05 liters.

02:04 Now for part b, we have to find the molecular weight in grams per mole.

02:12 We're given 1 .5 grams of an ideal gas.

02:16 Our v, our volume, is 500 milliliters, so let's change that to liters.

02:22 We're just going to divide by a thousand, so it's going to become 0 .500 liters.

02:28 Our pressure is in atmospheres already, so we don't have to worry about converting that, but our temperature was 75 degrees celsius, so we're going to have to convert this.

02:41 So that is going to be 348 kelvin.

02:47 Now let's take a look at the units for molecular weight, grams per mole...

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