I know i use PV=nRT...but when i plug it in it doesnt make sence...help???

Question

WHat is the volume of carbon dioxide in (c) if the presure is 785 mmHg and the temp is 30 degrees C? (R=62.43 mm x L/mol x K)

i think i use this somewhere but im not sure:

CaCO3→CaO + CO2

Answer 1

Volume = n x R x T / P

if you use pressure in mm Hg, V in liters, and T in deg K,  then R = 62.36.

CaCO3 --> CaO + CO2

If you know the mass of CaCO3 you can determine the moles of CaCO3 by dividing the mass by the molar mass of CaCO3 (100.09 g/mol). The moles of CO2 (n) equal the moles of CaCO3 (1 mol of CaCO3 = 1 mole of CO2). Use this value of n in the equation V = nRT/P  

Answer 2

We can't tell, because you don't give data from (c). If they give weight or moles, then use PV = nRT. If they give a previous volume, then use P1V1/T1 = P2V2/T2.

Answer 3

Your problem appears to be in the value you use for R

The gas constant (also known as the molar, universal, or ideal gas constant, usually denoted by symbol R) is a physical constant which is featured in a large number of fundamental equations in the physical sciences, such as the ideal gas law .

Its value is:

R = 8.314472(15) J · K-1 · mol-1

(there are other values for R, based on other units for the variables, but tis is what I have grown up with, and quoted in Wikipedia)

To use this costant in this form it is essential that:

1) Pressure is expressed in kPa (1atm = 760mmHg = 101.3kPa)

2) Volume is expressed in litres.

3) n is expressed in moles

4) Temperature is expressed in Kelvin = 273+ temp °C

Let us use this in your problem

Pressure = 785/760*101.3 = 104.63kPa

n = You have not given the mass of the CO2 or the moles. For illustration, assume the no of moles to be 0.575 moles

Temperature = 273+30 = 303K

Now substitute:

PV=nRT

104.63*V = 0.575*8.314*303

V = 0.575*8.314*303/104.63

V = 13.844litres.

To solve you problem, you must substitute the correct n in the equation.

If the question gives you the mass of the gas, you have to determine the moles by mass of gas/ molar mass of gas. use this result fot n

Answer 4

pv = nRT

R = 0.08206 (L*atm/mol*K)

pressure (P) - must always be expressed in terms of atm

since you were give pressure in mm Hg you have to convert mm Hg to atm. There is 1 atm in 760 mm Hg so,

785 mm Hg (1 atm / 760 mm Hg) = 1.03 atm

T (temperature) - must always be expressed in Kelvins (k). To convert from C to K, just add 273 to C so,

30 + 273 = 303 K

if you want to solve for v:

v = (nRT)/p, where n is the number of moles of gas.

You can find the number of moles of CO2 if you know how much CaCO3 you start with. Simply multiply the inverse of the molar mass of CaCO3 by the mass of CaCO3, then relate the moles of CO2 to the moles of CaCO3 to find the moles of gas.

g CaCO3 x molar mass of CaCO3 (inverse) x mol CO2/ mol CaCO3 = moles of CO2 gas

plug this value into the equation v = (nRT)/p

v = [n(0.08206 (L*atm/mol*K))(303 K)/1.03 atm] = x L

I think you should go with this method because it makes the most sense and alway works for me.