enthalpy of formation

9

hey, i'm quite confused with this question. would appreciate any help! thanks

enthalpy of formation:

Mg 5.103kJ
MgCO3 1.092kJ

H20 -286kJ
CO2 -394kJ

contruct an enthalpy cycle or diagram to show how the standard enthalpy of formation for MgCO3 can be calculated.

Apply Hess's law and calculate the standard enthalpy of formation for magnesium carbonate.

so, what owuld be the equation? do i actually need to use the enthalpy of formation of water and CO2?

i got the equation to be 2Mg + 2C + 3O2 -> 2MgCO3

where would the H2O and CO2 come into this? and they havent provided the value for C, or do i use the CO2 value for this? :confused:

thank you

Reply 1

moomoo2k

i can't remember how to do it but i can tell you that the value for any element in its standard state (i.e. Carbon as graphite, oxygen gas ) is 0 as no change is involved in forming them. that might help a little!
also, i think h2 gas is formed (Again will have a value of 0)...so that's how the water is put in...just think about the equation more.

Reply 2

ad absurdum

2

Remember that the enthalpy of formation of a compound is the energy required to form one mole of the compound from its elements in their standard states. You need to have a 1 (or no number is how its usually written) in front of the MgCO₃.

Reply 3

Eau

15

rozzy

hey, i'm quite confused with this question. would appreciate any help! thanks

enthalpy of formation:

Mg 5.103kJ
MgCO3 1.092kJ

H20 -286kJ
CO2 -394kJ

contruct an enthalpy cycle or diagram to show how the standard enthalpy of formation for MgCO3 can be calculated.

Apply Hess's law and calculate the standard enthalpy of formation for magnesium carbonate.

so, what owuld be the equation? do i actually need to use the enthalpy of formation of water and CO2?

i got the equation to be 2Mg + 2C + 3O2 -> 2MgCO3

where would the H2O and CO2 come into this? and they havent provided the value for C, or do i use the CO2 value for this? :confused:

thank you

How come you're already given the standard enthalpy of formation of MgCO3?

Also do you mean formation of Mg(g) from Mg(s)?

Reply 4

rozzy

OP

9

oh sorry, the values i gave are enthalpy change for the reaction of Mg and MgCO3, not enthalpy of formation. i need to find the enthalpy of formation for MgCO3

enthalpy of formation

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