Question

1.) For which of the following substances is the standard enthalpy of formation equal to zero?
a) water [H2O(l)] d) carbon dioxide [CO2(g)]
b) lead [Pb(l)] e) tin [Sn(s)]
c) carbon dioxide [CO2(s)]

2.) Consider the following four equations:
1. C6H6(l) + O2(g) 6CO2(g) + 3H2O(l) ΔH1
2. H2(g) + ½ O2(g) H2O(l) ΔH2
3. C(s) + O2(g) CO2(g) ΔH3
4. 6C(s) + 3H2(g) C6H6(l) ΔH4
The enthalpy change for reaction 1, ΔH1, can be obtained by combining the ΔH’s for the other reactions in which of the following ways?
a) 6(ΔH3) + 3(ΔH2) + ΔH4
b) 6(ΔH3) - 3(ΔH2) + ΔH4
c) 6(ΔH3) - 3(ΔH2) - ΔH4
d) 6(ΔH3) + 3(ΔH2) - ΔH4
e) none of these

3.) Which forces exist between hydrogen chloride particles?
I. London forces II. Metallic bonding III. Hydrogen bonding IV. Dipole-dipole
a) I only d) I, III and IV only
b) I and IV only e) I, II and III only
c) I and II only

Answer 1

OK. I've answered two questions that contained 3 problems each. I think you;ve had a chance to read my note to the first one by now. Here goes #1 ONLY.
Elements in their pure state at 25 C have DH = zero and 1 atm pressure are zero.