B. The heat of reaction for the process described in (a) can be determined by applying Hess's law. The heats of reaction shown in the table below can be obtained
experimentally or looked up in tables of enthalpy data. Which two of these heats of
reaction would be the easiest and safest to measure in the laboratory, and which two are
better obtained through reference sources? Why? Hint: Consider whether a reaction
takes place in aqueous solution or instead involves noxious gases.
Reaction
Heat of reaction
NH3(g) → NH3(aq)
AH= -34.64 kJ/mol
NH3(aq) + HCl(aq) → NH4+ (aq) + Cl(aq)
AH= -51.6 kJ/mol
HCI(g) → HCl(aq)
AH = -75.14 kJ/mol
AH = +14.8 kJ/mol
NH4Cl(s) → NH4+(aq) + Cl(aq)

a electronegativity decreases beacuse the size of nucleus is bigger.

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2