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secondary 4 | A Maths
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need help with this qn, pls explain too
Date Posted: 3 years ago
Views: 248
When the reactants collide effectively and react,
Number of C - H bonds broken = 2
Number of Cl - Cl bonds broken = 2
When forming the products :
Number of C - Cl bonds formed = 2
Number of H - Cl bonds formed = 2
Number of C - H bonds broken = 2
Number of Cl - Cl bonds broken = 2
When forming the products :
Number of C - Cl bonds formed = 2
Number of H - Cl bonds formed = 2
So,
Overall enthalpy change
= Net energy needed to break bonds - net energy released by forming bonds
= 2B.E(C - H) + 2B.E(Cl - Cl) - 2B.E(C - Cl) - 2B.E(H - Cl)
(B.E stands for bond energy)
= 2(410 kJ/mol) + 2(346 kJ/mol) - 2(340 kJ/mol) - 2B.E (H - Cl) = -30 kJ/mol
832 kJ/mol - 2B.E (H - Cl) = -30 kJ/mol
2B.E (H - Cl) = 832 kJ/mol + 30 kJ/mol
2B.E (H - Cl) = 862 kJ/mol
B.E (H - Cl) = 431 kJ/mol
Overall enthalpy change
= Net energy needed to break bonds - net energy released by forming bonds
= 2B.E(C - H) + 2B.E(Cl - Cl) - 2B.E(C - Cl) - 2B.E(H - Cl)
(B.E stands for bond energy)
= 2(410 kJ/mol) + 2(346 kJ/mol) - 2(340 kJ/mol) - 2B.E (H - Cl) = -30 kJ/mol
832 kJ/mol - 2B.E (H - Cl) = -30 kJ/mol
2B.E (H - Cl) = 832 kJ/mol + 30 kJ/mol
2B.E (H - Cl) = 862 kJ/mol
B.E (H - Cl) = 431 kJ/mol
Note that the C - C bond is not broken so they didn't give you its bond energy value.
And even if it was broken, it would be reformed so the B.Es on reactants side and products side will cancel out.
And even if it was broken, it would be reformed so the B.Es on reactants side and products side will cancel out.
thx :)
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done
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Updated solution (thks @J for the corrections)
Date Posted:
3 years ago
thx :)
done
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I rly suck at Chem so my answer might be wrong
Date Posted:
3 years ago
Forgot to divide by 2.
There are 2 net H - Cl bonds formed
There are 2 net H - Cl bonds formed
Oops
Delta H=BE of bonds broken-BE of bonds formed
So take the LHS minus the RHS
Also the table only gives some of the values needed so go to the data booklet for the rest of the values
So take the LHS minus the RHS
Also the table only gives some of the values needed so go to the data booklet for the rest of the values
No need. It's solvable as some bonds are not broken. i.e C - C bond.
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