28.1.14 Answers to bond energy questions

Please let me know after you have checked your answers if there is a problem.

Grade C Question. 

Hydrogen burns in chlorine.

H2(g) + Cl2(g)          2HCl(g)

a. One each of H–H and Cl–Cl bonds breaks.

b.  Two H–Cl bonds form.

c.  Energy to break bonds = 434 kJ + 242 kJ = 676 kJ

  Energy given out on forming bonds
  = 2 × 431 kJ = 862 kJ

  Overall energy change = -186 kJ given out.

d. Exothermic

Grade A Question 3.

a.  Bonds broken = 1933kJ

  Bonds formed = 1959kJ

  Overall energy = -26kJ

b.  Exothermic as the value is negative

Grade B Question 4

a.Negative amount of energy given out. So products have less energy than the reactants.

b.Is the minimum energy needed to start a reaction.

Grade A  to A* Question 5

c.i. 3466kJ/mol

c.ii. -730 kJ/mol

Have fun

27.1.14 This week's homework

Please see the NEW science online homework site and work through at least TWO of the homeworks set for C7 module.


http://kerboodle.oxfordsecondary.co.uk/users/login.
For username and password and website please refer to the school website, science department, resources. It's at the end of the list.
Any problems see me asap and email as well.

Please complete for Monday  3rd Feb..

Revision on new online homework

http://kerboodle.oxfordsecondary.co.uk/users/login?user_return_to=%2Fapp%2Fcourses%2F538%2Fmodules%2FHomework

Login in is initial and surname as one word lower case. and the same for the password