You throw a barbeque for your friends. Before you start the grill, your propane tank has a pressure of 78 psi. When you’re finished grilling, the temperature is 95°F and the propane tank reads 74 psi. Come nighttime the outside temperature drastically decreases to 20°C. What is the pressure of the propane tank at night? Select one:

a. 16 kPa

b. 485 kPa

c. 107 kPa

d. 2300 kPa

b. 485 kPa

Explanation:

Gay-Lussac's law express that the pressure of a gas under constant volume is directly proportional to the absolute temperature. The equation is:

P1T2 = P2T1

P is pressure and T absolute temperature of 1, initial state and 2, final state of the gas

Where P1 = 74psi

T2 = 20°C + 273.15 = 293.15K

P2 = ?

T1 = (95°F -32) * 5/9 + 273.15 = 308.15K

Replacing:

74psi*293.15K = P2*308.15K

70.4psi

In kPa:

70.4psi * (6.895kPa / 1psi) =

the answer is a

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