ADA Practice test

[sexysummer]

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Why is it choice B? Is ideal gas @ STP 0 Celsius and 1 atm?

Thanks

 

[goutamk]

When I took it I said that it was -273 C because that translates to 0 Kelvin and there should be no gas phase but only a solid.

 

[danchoi03]

When Ideal gas has no volume, you use PV = nRT formula to find that Temperature equals to zero Kelvin. Next you use the formula K = 273 + Celsius and you will find that Celsius is -273 deg C when Kelvin equals to zero.

 

[kobbix]

Is there a solid rule when to use 0.0821 vs 8.314?

 

[danchoi03]

for PV = nRT , you will want to use 0.0831 because the unit is L-atm / mole-K. Both volume and pressure are used in the equation. The R constant 8.314 is J/mole-K and there is no volume or pressure in there, so you cannot use this. When you are solving any chemistry problem, the first thing you will look at is the unit. This will give you clue how to solve the problem. Sometimes the unit even helps you eliminate the answer choices that are wrong.

 

[Frank22]

Is there a solid rule when to use 0.0821 vs 8.314?

A general rule would be to use 0.0821 when you're working with atmospheric pressure, and 8.314 when you're working with kilopascals.

 

[gooperwooper]

is the constant given to us or do we have to memorize it?

 

[Frank22]

is the constant given to us or do we have to memorize it?

Definitely memorize it.

 

[tyunup]

Do they ever provide you with constants? Like more obscure ones, ie. mass of an electron?

 

[Frank22]

Do they ever provide you with constants? Like more obscure ones, ie. mass of an electron?

No.