textbook 5.35

[Talia Leano 2H]

How do you determine this is 2A -> 2B + C ?

[Ritika Prasad 1A]

I believe the solution manual states that the answer to part a would be: 2A --> B + 2C.

According to the graph, looking at the changes in pressure from initial state to equilibrium, ΔA = 10, ΔB=5, and ΔC=10.

From this, the ratio of change in A:B:C would be 2:1:2. This ratio then provides the coefficients for the reactants and products in the equation and since this is decomposition of A into B and C, the equation would be 2A --> B + 2C.

[Adrienne Yuh 2B]

I was also wondering this, but the relative ratios of change (delta) creates the 2:1:2 pattern.

[allyssa bradley 1H]

I believe the solution manual states that the answer to part a would be: 2A --> B + 2C.

According to the graph, looking at the changes in pressure from initial state to equilibrium, ΔA = 10, ΔB=5, and ΔC=10.

From this, the ratio of change in A:B:C would be 2:1:2. This ratio then provides the coefficients for the reactants and products in the equation and since this is decomposition of A into B and C, the equation would be 2A --> B + 2C.

Hey Ritika, this description was super helpful to me! I was just focused on those end values, which clearly are pretty weird. Sorry for dredging up your post from over a month ago and it's ok if you can't answer this question, but do we use the end values the reaction plateaus on for our K value? Even with the new coefficients, my K value doesn't quite match what the book has, so I feel like I'm still messing something up.

[Ritika Prasad 1A]

Hey Ritika, this description was super helpful to me! I was just focused on those end values, which clearly are pretty weird. Sorry for dredging up your post from over a month ago and it's ok if you can't answer this question, but do we use the end values the reaction plateaus on for our K value? Even with the new coefficients, my K value doesn't quite match what the book has, so I feel like I'm still messing something up.

Hey Allyssa! I'm glad that explanation helped! For the K value, yes, I believe you would use the end values because those are the values at equilibrium, so K = [(Partial Pressure of B)*(Partial Pressure of C)^2]/[(Partial Pressure of B)^2] so in simplified form: K = [(B)(C^2)]/[(A^2)].

Since we're not given exact values at the end, we can estimate from the graph that the partial pressure of A is 18, C is 10, and B is 5.

In the solution manual, I believe the values are divided by 100 because the y-axis scale is P/kPa, and standard atmospheric pressure (or 1 atm) is defined as 101.325 kPa.

So then finally, you get [(5/100)*(10/100)^2]/[(18/100)^2] = 1.54 x 10^-2, which matches the solution in the manual! I hope that helps :)