You have a series of four chemical reactions (1→2→3→4).
How do you calculate the ΔH2 if you know the other ΔH values?

ΔH2=ΔH1+ΔH3 + ΔH4

ΔH2=(ΔH1)(ΔH3)/ (ΔH4)

ΔH2=ΔH4−(ΔH1 + ΔH3)

ΔH2=ΔH1+ΔH3 − ΔH4

Explanation:

The question must be restated because you can calculate ΔH₂ from the other reactions only if you know the global ΔH, ΔH₁, and ΔH₃.

As stated by Hess’s law, the overall change in the enthalpy, ΔH, of a reaction does not depend of the path followed.  Thus, when you have a series of reactions,  the net change from the first reaction to the last reaction is equal to the sum of the ΔH values for the individdual reactions:

If you name ΔH₄, the overal change in the enthalpy to convert 1 to 4, but ΔH₁, ΔH₂, and ΔH₃ are the changes of the intermediate reactions that transform 1 in 2, 2 in 3, and 3 in 4, respectively, then, you can write, accordingly to Hess's law, you can write:

Then, assuming you know ΔH₄, ΔH₁, and ΔH₃, you can calculate ΔH₂ clearing from the previous equation:

given:

mass of na = 115 g

excess cl2

to determine:

mass of nacl produced

explanation:

given reaction is-

2na(s) + cl2(g) → 2nacl(s)

since cl2 is in excess, na will be the limiting reagent

as per the reaction stoichiometry na: nacl = 1: 1

i.e. moles of na reacted = moles of nacl formed

now, # moles of na = mass of na/atomic mass

                                  = 115 g/23 g.mol-1 = 5 moles

therefore, moles of nacl = 5

molar mass of nacl = 58 g/mol

mass of nacl = 5 moles * 58 g.mol-1 = 290 g

ans: amount of nacl produced = 290 g

a polar bond is formed when electrons are shared unevenly between atoms