Chemistry Forum

If you were to react a given quantity of calcium carbide with a given amount of water in a closed container of known volume, can you calculate the resulting gas pressure? Both before and after the heat of reaction has dissipated? Will equilibrium be reached at some pressure between the unreacted materials and the acetylene gas? I.E. is there a maximum possible pressure for this reaction at a given temperature?
Any help would be greatly appreciated!

Write and balance the reaction: CaC₂ + H₂O -- > Ca(OH)₂ + C₂H₂

1 mol of CaC₂ will produce 22.4 L of acetylene. Squeeze it to 11,2 L and get 2 atm pressure and so on.

Thank you, that will certainly get me started. I'm trying to figure out if there is an equilibrium state at some pressure, or if there is no limit to pressure generated. It's been a long time since thermodynamics...
Bryan

Wikipedia is back today, so read about Gas Laws http://en.wikipedia.org/wiki/Ideal_gas_law

OK. I've calculated the amount of gas produced, and the pressure increase due to the volume of the container vs free volume of the gas.
I want to figure out the pressure after reaction.
Since this is an exothermic reaction, heat will be produced which will raise the temperature of the system.

I found this explanation:
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2H₂O > 2H₂ +O₂...............-H= 2* -285.83
Ca + O₂ + H₂ > Ca(OH)₂....H= -986.2
2C + H₂ > C₂H₂.................H= 226.77

The above H's stand for standard enthalpy of formations. These can be found in textbook appendix. Notice the negative infront of the enthalpy (H) for H₂O. This is to remind you that the heat lost is gained in the rxn.

So then you add them up. 226.77 - 986.2 + (2*285.83) = -187.77

Add back the total enthalpy that is given in the question -187.77+127.2 = -60.57
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So, is the -60.57 the heat of formation for one mol of acetylene produced from this reaction?

Does the 22.4 liters/mol include this heat of formation, or is this volume after the heat has dissipated? Is this value at room temperature?

In other words, I react a certain amount of CaC₂ with excess water to form a given volume of gas at 1 bar. But the reaction actually takes place in a given volume. So do I have to account for the heat of formation in addition to the heating that occurs from compression of the gas to figure out the final temperature, which will increase the pressure obtained?

Any help/direction would be most appreciated, my head is swimming!

I think I answered my question about equilibrium, if the pressure gets high enough, the gas will form a liquid with the pressure equal to the vapor pressure of the liquid at the given temperature. Presumably all the CaC₂ will react as long as the volume isn't so small that the pressure would create a solid.

Thanks,
Bryan