# Chemistry Questions: Gases and Gas Reactions

A balloon contains 400cm3 of helium at 25 degrees and 1 atm pressure. If the balloon bursts when the volume exceeds 800cm3:

a) What would be the maximum temperature it could withstand at constant pressure?

b) What would be the minimum pressure it could withstand at constant tempersture?

c) What height above sea level would the answer to b) represent if the air pressure falls by 0.1atm per 1000 feet?

2. The following results were obtained in the practical determination of the relative molecular mass of a gas.

A gas syringe was sealed containing 5cm3 of air. Its mass was found to be 150.00g. a dry sample of gas was drawn into the syringe until the total volume was 100cm3, when the syringe was sealed again. The mass of the syringe containing the air and gas mixture was 150.124g.

If the room temperature was 21degrees and the pressure was 755 mm Hg calculate the relative molecular mass of the gas (standard pressure = 760 mm Hg, standard temp 273K. Molar volume of gas 22.4 dm3 at STP)

3. Hydrogen sulphide burns in oxygen in accordance with the following equation:

2 moles hydrogen sulphide(g) + 3 moles of oxygen gas forms 2moles of water gas and 2moles of sulphur dioxide gas

If 8 litres of hydrogen sulphide are burnt in 20 litres of oxygen at 760 mm Hg pressure and a temperature of 600k, what will be the final volume, in litres, of the gaseous mixture under these conditions?

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#### Solution Preview

Response 1:

(a) The first thing we need to do is calculate the number of moles, n, of He in the balloon. How can we do this? We use the ideal gas equation, PV = nRT. But, we rearrange it to solve for n.

n = PV/RT

What do we know?

P = 1 atm

V = 400 cm3 = 400 mL = 0.400 L

T = 25 C = 298 K

R = 0.08206 L-atm/mol-K

Now, we plug them in and calculate n.

n = PV/RT = (1 atm)(0.400 L)/(0.08206 L-atm/mol-K)(298 K) = 0.0164 moles of He

Now, what to do we? We want to know the maximum temperature that could be sustained before the balloon bursts. We know it bursts at 0.800 L volume. Therefore, we use the ideal gas equation again, but this time solving for T.

T = PV/nR

What do we know?

V = 0.800 L

P = 1 atm

R = 0.08206 L-atm/mol-K

n = 0.0164 mol

T = (1 atm)(0.800 L)/(0.0164 mol)(0.08206 L-atm/mol-K) = 594 K

Therefore, if the temperature goes above 594 K (which is 321 degrees C), the balloon will burst.

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(b) To determine the minimum pressure, we do the same thing that already did, except this time, we keep the temperature fixed and find out what the ...

#### Solution Summary

This solution provides step by step calculations for various questions regarding gases and their reactions.