Consider the reaction: 2CO2(g)=2CO(g) + O2(g). A reaction mixture in a 5.0 L flask at a certain temperature. At equilibrium there are 85 g of CO2(g), 1.20 g of CO, and 0.688 g of O2(g). Calculate Kc.

Kc = (CO)^2(O2)/(CO2)^2

Convert grams given to moles. moles = grams/molar mass. Convert to molarity from moles/5.0, then substitute into the Kc expression above and calculate Kc.

To calculate the equilibrium constant, Kc, for this reaction, we need to use the concentrations of the reactants and products at equilibrium.

We are given the mass of each substance at equilibrium: 85 g of CO2, 1.20 g of CO, and 0.688 g of O2. However, to calculate the concentrations, we need to convert these masses into moles.

First, we need to find out the molar masses of each substance:
- Molar mass of CO2 = 12.01 g/mol (C) + 2 * 16.00 g/mol (O) = 44.01 g/mol
- Molar mass of CO = 12.01 g/mol (C) + 16.00 g/mol (O) = 28.01 g/mol
- Molar mass of O2 = 2 * 16.00 g/mol (O) = 32.00 g/mol

Next, we can calculate the number of moles of each substance:
- Moles of CO2 = mass of CO2 / molar mass of CO2 = 85 g / 44.01 g/mol = 1.931 mol
- Moles of CO = mass of CO / molar mass of CO = 1.20 g / 28.01 g/mol = 0.0428 mol
- Moles of O2 = mass of O2 / molar mass of O2 = 0.688 g / 32.00 g/mol = 0.0215 mol

Now, we can calculate the concentrations (in mol/L) by dividing the number of moles by the volume of the flask (5.0 L):
- Concentration of CO2 = Moles of CO2 / Volume of flask = 1.931 mol / 5.0 L = 0.386 M
- Concentration of CO = Moles of CO / Volume of flask = 0.0428 mol / 5.0 L = 0.0086 M
- Concentration of O2 = Moles of O2 / Volume of flask = 0.0215 mol / 5.0 L = 0.0043 M

Finally, we can substitute these values into the equation for Kc:
Kc = (CO)^2 * (O2) / (CO2)^2

Kc = (0.0086)^2 * (0.0043) / (0.386)^2

After calculating this expression, we find the value of Kc for the reaction.