Gen Chem questions

[urDDS]

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I remeber some books saying that :

CaC03(s)>>> Cao(s) + CO2(g), what happens to system when pressure added, I thought nothing since both CaCO3 and Caos are soilds, but the answer said decreasing CaO and Co2??????

2) a question asked how many calories are required to melt 12 g of NaCl? they gave heat of fusion=7250 cl/mol. and answe 1500 ????

3) how you balance
I2 +6H2O>>> 2IO3 + 12H+ + (?)e-

 

[adizzle87]

Increasing pressure is pretty much decreasing volume. Since your # of mol of CO2 is the same but your volume is decreasing, the [CO2] goes up. This is against equilibrium and to bring it back to back to equilibrium you must decrease the amount of CO2. According to that equation the only way to do it is to react it with CaO (it doesn't matter what the phase is).

 

[daehyuny]

its Le Chateliers principle..

Always this when heat is added, the equillibrium will shift to undo it
By shifting to endothermic direction,

Just like that, if the pressure is added, the equillibrium will shift to undo the pressure
by shifting to side with no gas ( no pressure)

When equillibrium is disturbed, ther reaction will shift do either side to undo whatever it did.

 

[bigstix808]

2) a question asked how many calories are required to melt 12 g of NaCl? they gave heat of fusion=7250 cl/mol. and answe 1500 ????

12 g NaCl (1 mol \ 58.5 g) * (7250 cal / mol) = 1487 ~ 1500 cal

 

[khakwanit1]

The phase does matter

 

[Sublimation]

for the last part it should be 12e to make up for the 12protons. both sides are neutral.

 

[iwannabadentist]

12 g NaCl (1 mol \ 58.5 g) * (7250 cal / mol) = 1487 ~ 1500 cal

i always thought the equation was:
q = mC(delta)T
m = moles
c = specific heat
both of which you included in the equation
but what about deltaT? dont you need to factor that in?

and if your are still confused abt the CaCO3 question....anytime pressure is increased in an equation, the equation will shift as to reduce the number of moles (and thus reducing the amount of pressure). but rmmr...the reduction in the number of moles only applies to gases because solids and liquids are not affected too much by pressure because they cannot be compressed beyond a certain point...which makes it negligible to account for these phases when considering pressure.

 

[chessxwizard]

For the first second question, you just have to take into consideration the phase change from solid to liquid at fusion temperature.

 

[bigstix808]

i always thought the equation was:
q = mC(delta)T
m = moles
c = specific heat
both of which you included in the equation
but what about deltaT? dont you need to factor that in?

and if your are still confused abt the CaCO3 question....anytime pressure is increased in an equation, the equation will shift as to reduce the number of moles (and thus reducing the amount of pressure). but rmmr...the reduction in the number of moles only applies to gases because solids and liquids are not affected too much by pressure because they cannot be compressed beyond a certain point...which makes it negligible to account for these phases when considering pressure.

i think the question assumed that the NaCl is at the temp of fusion thus the deltaT=0. (only assumed b/c they do not give any other information)

so in this case you would use q=mc

 

[peyman2002]

i think the question assumed that the NaCl is at the temp of fusion thus the deltaT=0. (only assumed b/c they do not give any other information)

so in this case you would use q=mc

m is not equal to mole, its equal to mass (g) thus q=mc wouldnt work here