Agas sample of argon, maintained at constant temperature, occupies a volume of 500. l at 4.00 atm. what is the new volume if the pressure were charged to 8.0 atm

Boyle's law gives the relationship between pressure and volume of gas. 
It states that at constant temperature, pressure is inversely proportional to volume of gas.
PV = k
where P - pressure, V - volume and k - constant 
P1V1 = P2V2
where parameters for the first instance are on the left side and parameters for the second instance are on the right side of the equation 
substituting these values in the equation 
4.00 atm x 500 L = 8.0 atm x V
V = 250 L 
new volume is 250 L

Spontaneity tell us the direction of the reaction, but not how fast it goes. gibbs free energy brings together enthalpy, entropy and temperature in one easy formula. g = h - ts. and, finally the sign of delta g is always negative for a spontaneous reaction.