At equilibrium for 2SO2 + O2 forming 2SO3, [SO2] = 0.90 M, [O2] = 0.35 M and [SO3] = 1.1 M. What is Kc?

1. Write the expression: Kc = [SO3]^2 divided by ([SO2]^2 x [O2]). 2. Numerator: 1.1 x 1.1 = 1.21. 3. Square the sulfur dioxide term: 0.90 x 0.90 = 0.81. 4. Multiply by the oxygen term: 0.81 x 0.35 = 0.2835. 5. Divide: 1.21 / 0.2835 = 4.27, which rounds to Kc = 4.3. 6. Dropping the square on sulfur trioxide alone would give roughly 3.9, not an offered value. 7. The value 1.2 comes from taking the numerator and forgetting to divide at all. 8. The value 0.23 is the reciprocal, which describes the reverse reaction instead. _Source: OpenStax Chemistry (CC BY 4.0), Ch 13 "Fundamental Equilibrium Concepts", section 13.2 Equilibrium Constants_