Energy changes in chem react
2011-03-13 12:27 am
2.00 g of sulphur were completely burnt in air. The heat given off raised thetemperature of 222 g of water from 21 degree celsius to 41 degree celsius.Calculate the enthalpy change of combustion of sulphur, in KJ mol^-1.( Relative atomic mass: S = 32.1; specific heat capacity of water = 4.18J g^-1 K^-1 )Ans: 297.9KJ mol^-1
回答 (3)
2011-03-13 12:57 am
✔ 最佳答案
Energy given out = 222*4.18*(41-21) = 18559.2 Jmol sulphur present = 2/32.1=0.062 mol
so the enthalpy change = 18559.2/0.062 = 297875.16 J ≈ 297.9KJ/mol
2011-03-13 9:06 am
note that the enthalpy change should be negative, i.e. exothermic.
2011-03-13 12:58 am
Heat released
= mcΔT
= -(222)(4.18)(41 - 21)
= -185559.2 J = -18.56kJ
No. of moles of sulphur
= 2 / 32.1 = 0.06231 mol
Enthalpy change of combustion of sulphur
= -18.56 / 0.06231
= -297.9 kJ mol^-1
2011-03-12 17:08:54 補充：
Typing mistake:
Heat released = -18559.2 J = -18.56kJ
= mcΔT
= -(222)(4.18)(41 - 21)
= -185559.2 J = -18.56kJ
No. of moles of sulphur
= 2 / 32.1 = 0.06231 mol
Enthalpy change of combustion of sulphur
= -18.56 / 0.06231
= -297.9 kJ mol^-1
2011-03-12 17:08:54 補充：
Typing mistake:
Heat released = -18559.2 J = -18.56kJ
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