In the ideal gas law PV=nRt, what is R?
To know what is R we need to go back to the “ Combined Gas Law Equation”. While deriving this equation we got to knew that PV/T = k., where k is proportionality constant. So, when one gram of gas is taken then value of ‘k’ will vary from one gas to another and is known as specific gas constant.When one mole of gas is taken then every gas will have same value of ‘k’ and is denoted by ‘R’ which is known as universal gas constant.When pressure is in atmosphere, volume is in litre and temperature is in kelvin scale, then R = 0.0821 litre.atm .mol^-1.k^-1
What units does one use with the equation PV=nRT?
I recommend memorizing two values for R.. R = 0.08206 Latm/moleK and R = 8.314 J/moleK and then learning to convert units of volume, P and T to L, atm, K. example... if I have P in mmHg? I convert it to atm... like this... P = __ mmHg x (1atm / 760mmHg) = ___ atm
Need help with the formula PV=nRT please.?
look at "futures" answer. there are what? 15 different variations of "R" listed there? Do you want to carry around a crib sheet with all of those? Or, heaven forbid, MEMORIZE all those?.. Not me! It's easier to memorize R = 8.314 J/moleK and R = 0.08206 Latm/moleK and then convert P, V, and T units as you need to. the J/moleK version works well with things like Clausius Clapeyron equation. The Latm/moleK works well with equations of state (like the ideal gas laws, all the variations of P1V1 / n1T1 = P2V2 / n2T2, Van Der Walls, osmotic pressure, etc) Probably >90% of your chemistry life will be spent working with the Latm/moleK. The reason your instructor gave you BOTH versions is many students have trouble converting from J/moleK to Latm/moleK. How do you convert J to Latm? (notice I left off the moleK? both J/moleK and Latm/moleK have moleK in the denominator. So we only need to focus on the numerator)...watch... 1 J = 1 kg m² / s² 1 atm = 101325 N / m² 1 N = 1 kg m / s² 1000 L = 1 m³ 8.314 J x ((1 kg m² / s²) / 1 J) x (1 N / (1 kg m/s²)) x = 8.314 N m 8.314 N m = 8.314 N m³ / m² 8.314 N m³ / m² x (1000 L / 1 m³) = 8.314 (N/m²) x L x (1 atm / 101325 N/m²) = 0.08205 Latm... it's complicated right? so you memorize 8.314 J/moleK and 0.0821 Latm/moleK...And you USUALLY use 0.08206 Latm/moleK *************************** your problem.... PV = nRT n = PV / RT where... P = 99.8 kPa x (1 atm / 101.325 kPa) = 0.985 atm V = 90.0 mL x (1 L / 1000 mL) = 0.0900 L R = 0.08206 Latm/moleK T = 35.0 C = 35.0 + 273.15 K = 308.2 K (notice the conversion techniquie? "factor label method" aka "dimensional analysis". LEARN IT. it's important) n = (0.985 atm) x (0.0900 L) / [(0.0821 Latm/moleK) x (308.2 K)] n = 3.50x10^-3 moles ************** questions?
(P1*V1)/T1=(P2*V2)/T2 ; T is K's, V is L's, but is P Pa, atm, or psi?
doesn't matter. just use the same pressure units on both sides of the equation. Now, if you write this out as PV=nRT then you have the gas constant, R, which does have units and essentially it helps you convert moles and degrees K into whatever pressure and volume units you have on the Left Hand Side. Normally with PV=nRT P would be in atmospheres -the gas constant would then be 0.082 -at least that is the value I used many many times. <>http://scienceworld.wolfram.com/physics/UniversalGasConstant.html> has a list of R in various units. Let me also point out that in the form (P1*V1)/T1=(P2*V2)/T2 the units of pressure do not matter the units of V do not matter the units of T do not matter (as long as 0 on the temperature scal is absolute 0) This means you can sometimes solve these ideal gas problems really quickly because you don't need to convert units and pick out a gas constant etc. And the number of moles doesn't need to be factored in as long as it is not changing.
How do you determine which gas constant to use for a certain problem?
You should use each constant when the data in the problem are those in the constant. e.g. If you have L, atm, K and moles, you can use the first one, if you have cal, K and moles, you should use the last one. What I would recomment is to find out how to convert some things, so that you can only use one constant. I, for example, always use the first one. I turn the volume into Litres (don't forget,1dm3=1L), the temperature in Kelvin (0 centigrades = 273 K) and the same goes for 1 atm, which equals 1 atm = 101325 Pascals. This way, you will always have the data in the same units and you'll only have to remember the first one. :)