A gas originally at a pressure of 791 mm Hg and a volume of 500.0 mL is allowed to expand to 1.00 Liter. What is the new pressure of the gas? (Boyle)

The new pressure of the gas is 395.5mmHg

Explanation:

The pressure of a gas is inversely proportional to its concentration (Boyle's law). The equation that explain this law is:

P₁V₁ = P₂V₂

Where P is pressure

And V is volume of 1, initial state and 2, final state of the gas

Initial state:

791mmHg; 0.500L.

Final state:

1.00L

Replacing:

791mmHg* 0.500L = P₂*1.00L

P₂ = 395.5mmHg

n2(g) + 3h2-> 2nh3(g)   this is the balanced equation

note the mole ratio between n2, h2 and nh3.   it is 1 : 3 : 2   this will be important.

moles n2 present = 28.0 g n2 x 1 mole n2/28 g = 1 mole n2 present

moles h2 present = 25.0 g h2 x 1 mole h2/2 g = 12.5 moles h2 present

based on mole ratio, n2 is limiting in this situation because there is more than enough h2 but not enough n2.

moles nh3 that can be produced = 1 mole n2 x 2 moles nh3/mole n2 = 2 moles nh3 can be produced

grams of nh3 that can be produced = 2 moles nh3 x 17 g/mole = 34 grams of nh3 can be produced

note:   the key to this problem is recognizing that n2 is limiting, and therefore limits how much nh3 can be produced.

the answer to your question is c.

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