# Chem questions.

#### ~angel~

Just having trouble again with a few questions.

1.Calcium oxide (lime) is a white crystalline solid with a melting point of
2572c. It is manufactured by heating limestone, coral, sea shells or
chalk, which are mainly CaCO3, to drive off carbon dioxide, according to
the following reaction.

CaCO3(s) --> CaO(S) + CO2(g) Kp= 1.16 atm at 800c

If 20.0g of CaCO3 were sealed in a 10.0L container and heated to 800c, what
percentage of CaCO3 would remain unreacted at equilibrium?

2.A saturated solution of iodine in water contains 0.330g I2 per litre, but
more than this amount can dissolve in a potassium iodide solution because
of the following equilibrium.

I-(aq) + I2(aq) <--> I3- (aq)

A 0.100 M KI solution dissolves 12.5g of I2 per litre, most of which is
converted to I3-(aq). Assuming that the concentration of I2(aq) in all
saturated solutions is the same, calculate the equilibrium constant for
the above reaction.

I know Kc= [I3-]/[I-][I2], but I don't know where to go from there.

3. What is the longest wavelength of light that the ground state C2+ ion will
absorb? For this question, an MO diagram is given with energy in electron volts. I'm assuming you need to convert the energy in to joules (multiply by 1.602*10^-19) and use E=hc/lambda, but I don't know where to measure the energy from.

Any help would be great.

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#### Astronuc

Staff Emeritus
~angel~ said:
1.Calcium oxide (lime) is a white crystalline solid with a melting point of
2572c. It is manufactured by heating limestone, coral, sea shells or
chalk, which are mainly CaCO3, to drive off carbon dioxide, according to
the following reaction.

CaCO3(s) --> CaO(S) + CO2(g) Kp= 1.16 atm at 800c

If 20.0g of CaCO3 were sealed in a 10.0L container and heated to 800c, what
percentage of CaCO3 would remain unreacted at equilibrium?
How many moles of CO2 would produce 1.16 atm at 800°C in 10L, ignoring the volume of 20 g of CaCO3?

#### ~angel~

Ok, I get it. Thanks.

#### ~angel~

Does anyone know how to do questions 2 and 3 (particularly 2)?

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