[Kuahji]

When baking soda is heated it decomposes according to the following reaction:
2 NaHCO3 (s) -> Na2CO3 (s) + H2) (g) + CO2 (g)

If sufficient baking soda is placed in a container and heated to 90 degrees Celsius, the total pressure of the gases is .5451 atm. What is the value of Kp at that temperature.

So the professor shows the work Kp=[P H2O][P CO2]
this much I agree with.

But then the next step he shows
PH2O=PCO2= .5451/2=.2726
Kp=(.2728)^2=.07428

Is this actually correct. I don't see how you can "assume" the partial pressures are equal to one another. Or can you? I mean why can't the partial pressure of water at that temperature be something like say .3 & CO2 be .2451?

[Borek]

I don't see how you can "assume" the partial pressures are equal to one another.

Take a look at the reaction equation, it is all in stoichiometry.

[AWK]

2 NaHCO3 (s) -> Na2CO3 (s) + H2) (g) + CO2 (g)

Wrong equation, should be H2O instead of H2

Is this actually correct. I don't see how you can "assume" the partial pressures are equal to one another.?

Look at stoichiometry of reaction.
What Avogadro law says?