Diamond and graphite are two cystalline forms of carbon. At 1 atm and 25°C, diamond changes to graphite...?

May 2021 1 293 Report

Diamond and graphite are two cystalline forms of carbon. At 1 atm and 25°C, diamond changes to graphite...?

...so slowly that the enthalpy change of the process mst be obtained indirectly. Determine ∆H rxn for:

C(diamond) ---> C(graphite)

with equations from the following list:

(1) C(diamond) + O2(g) --> CO2(g) ∆H= -395.4 kJ

(2) 2CO2(g) ---> 2CO(g) + O2(g) ∆H= 566.0 kJ

(3) C(graphite) + O2(g) ---> CO2(g) ∆H= -393.5 kJ

(4) 2CO(g) ---> C(graphite) + CO2(g) ∆H= -172.5 kJ

Asia,

The only two equations you need out of this list are (1) and (3):

(1) C(diamond) + O2(g) --> CO2(g) ∆H= -395.4 kJ

(3) C(graphite) + O2(g) ---> CO2(g) ∆H= -393.5 kJ

If we reverse equation (3), we get

(3') CO2(g) --> C(graphite) + O2(g) ∆H= +393.5 kJ

Add equation 1 to equation 3', cancel out the common terms for CO2 and O2, and you get

(1) C(diamond) + O2(g) --> CO2(g) ∆H= -395.4 kJ

(3') CO2(g) --> C(graphite) + O2(g) ∆H= +393.5 kJ

C(diamond) ---> C(graphite) ∆H= -1.9 kJ

or conversely,

C(graphite) ---> C(diamond) ∆H= 1.9 kJ

Doesn't seem like ***that*** much to make diamonds; maybe we can go into business??? Hope that helped!