Answer:-
7.03 g
Explanation:-
Let the mass of water needed be M.
So total mass = M + 0.37
Now 5% of this solution has 0.37g of rubidium chlorude.
∴ (M +0.37) x (5/100) = 0.37
M +0.37 = 0.37 x 100/5
M + 0.37 = 7.4
M = 7.4-0.37
=7.03
Thus water to be added is 7.03 gram
ΔHrxn = ΣδΗ(bond breaking) - ΣδΗ(bond making)
Bond enthalpies,
N ≡ N ⇒ 945 kJ mol⁻¹
N - Cl ⇒ 192 kJ mol⁻¹
Cl - Cl⇒ 242 kJ mol⁻¹
According to the balanced equation,
ΣδΗ(bond breaking) = N ≡ N x 1 + Cl - Cl x 3
= 945 + 3(242)
= 1671 kJ mol⁻¹
ΣδΗ(bond making) = N - Cl x 3 x 2
= 192 x 6
= 1152 kJ mol⁻¹
δHrxn = ΣδΗ(bond breaking) - ΣδΗ(bond making)
= 1671 kJ mol⁻¹ - 1152 kJ mol⁻¹
= 519 kJ mol⁻¹
If you think of it endothermic is when there is energy needed for the reaction to occur and exothermic is when the reaction releases energy
