Answer:
49.82414 atm
50.74675 atm
Explanation:
P = Pressure
V = Volume = 5.45 L
R = Gas constant = 0.08205 L atm/mol K
T = Temperature = 25°C
a = 0.211 atm L²/mol²
b = 0.0171 atm L²/mol²
From ideal gas law we have
The pressure is 49.82414 atm
From Van der Waals equation we have
The pressure is 50.74675 atm
First of all, we need to write the First Law of thermodynamics assigning the correct sign convention:
where
is the change in internal energy of the system
Q is the heat absorbed/released
W is the work done
and the signs are assigned based on whether there is an increase in the internal energy or not. Therefore:
Q is positive if it is absorbed by the system (because internal energy increases)
Q is negative if it is released by the system (because internal energy decreases)
W is negative if it is done by the system on the surrounding (because internal energy decreases)
W is positive if it is done by the surrounding on the system (because internal energy increases)
Using these definitions, we can now fill the text of the question:
When a system is heated, heat is ABSORBED by the system. The amount of heat added is given a POSITIVE sign. When a system is cooled, heat is RELEASED by the system. The amount of heat is given a NEGATIVE sign. If a gas expands, it must push the surrounding atmosphere away. Thus, work is done BY the system and is given a NEGATIVE sign. If a gas is compressed, then work is done ON the system. This work is given a POSITIVE sign.