[Chocotaco]

I have a question here which I'm not quite sure how to tackle.

Oxyacetylene torches used in high-temperature welding use a combination of oxygen and acetylene. The combustion of acetylene (C2H2) occurs in these torches. What volume of acetylene is reacted if 250 mL of oxygen is consumed in the reaction?

I literally have no idea how to do this, every other problems were pretty understandable except this.

and

255 ml of hydrogen are at/under a pressure of 950 torr. If the pressure is changed to 1140 torr, under constant temperature-quantity conditions, the volume of the hydrogen will increase? or decrease?

This one I'm not so sure either (Edit: Going by Boyle's Law, the volume will decrease according to increase in pressure. Pretty sure)

Any help would be great.

[Schrödinger]

You got the 2nd one right. (the one regarding H₂)

For the 1st question, start by writing the balanced chemical equation for the combustion of C₂H₂.

[Chocotaco]

Thanks, ya I kinda figured you needed to write a balanced equation, after that it all came together. I wasn't really expecting that.

But I have another question although it's different from gas laws, and I don't really want to make another topic to clutter. Just need some assurance for this.

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Calcium releases red light as a result of an electron transition within the calcium atom. How much energy is released if radiation of n = 4.66 x 10^14 Hz is released by 0.338 mol of calcium atoms ?

Using Bohr E= h*frequency  so E= 6.626e-34(4.66e14) would give me 3.087e-19 Joules

I'm not sure if that's the right final answer, mainly cause the .338 mol of calcium is bothering me, also it feels too easy.

[Schrödinger]

Calcium releases red light as a result of an electron transition within the calcium atom. How much energy is released if radiation of n = 4.66 x 10^14 Hz is released by 0.338 mol of calcium atoms ?

Using Bohr E= h*frequency  so E= 6.626e-34(4.66e14) would give me 3.087e-19 Joules

That is the energy released by one Ca atom. Now you have 0.338 mol of Ca atoms. So total number of Ca atoms = 0.338 * Avogadro's number.

[Chocotaco]

Ok so I would have 2.036e23 Carbon atoms.  So I would have to multiply that into 3.087e-19 and get 6.28e4 J for final? Hopefully that's how it is.

[Schrödinger]

Yes. That is correct