[jessica Gwin]

Could someone please help me with these two questions. Thank you!!

1. Explain: The Heat of Combustion of Magnesium is the same as the Heat of Formation of Magnesium Oxide.

2. The following results were obtained for a typical, simple, calorimetry lab to find the heat of reaction for the combustion of a fuel Propane (C₃H₈)
       
        Mass of water in calorimeter       = 150g
        Initial mass of burner + fuel       = 146.56g
        Final mass of burner + fuel        = 145.77g
        Initial temp of water                 = 297.5K
        Final temp of water                  = 309.5K

Calculate the Heat of Combustion for the fuel, and give two reasons why the result is likely to be low.

[mrdeadman]

for number one: i think, but im not exactly 100% sure on this. when magnesium combusts, it reacts with O₂ to form magnesium oxide which is why it is the same value.

[xiankai]

for number one, i think mrdeadman's reply sounds OK

for number two, think about how u calculated the heat produced, and where the rest of the heat went

[Donaldson Tan]

1. Explain: The Heat of Combustion of Magnesium is the same as the Heat of Formation of Magnesium Oxide.

They are the same process.

2. The following results were obtained for a typical, simple, calorimetry lab to find the heat of reaction for the combustion of a fuel Propane (C₃H₈)
       
        Mass of water in calorimeter       = 150g
        Initial mass of burner + fuel       = 146.56g
        Final mass of burner + fuel        = 145.77g
        Initial temp of water                 = 297.5K
        Final temp of water                  = 309.5K

Calculate the Heat of Combustion for the fuel, and give two reasons why the result is likely to be low.

Assume all fuel (propane) was consumed and the reaction route is complete combustion.

Hence, mass of fuel = 156.66g - 145.56g

Heat released by combustion = heat absorbed by water = m.c.dT where
m: mass of water
c: specific heat capacity
dT: increase in temperature of water.

Why does this procedure produce an underestimate?

1. Is all heat of reaction being absorbed by water
2, Is it necessary complete combustion that occur in the calorimeter?