Answer:
155 kJ
Explanation:
The energy change will be the energy of the reactants less the energy of the products. And the energy of each compound is the sum of the energy of their bonds. Let's call y the N-Br strength.
3HOBR = 3x(459 + 201) = 1980 kJ
NH₃ = 3x386 = 1158 kJ
3H₂O = 3x(2x459) = 2754 kJ
NBr₃ = 3y
3y + 2754 - 1158 - 1980 = 81
3y -384 = 81
3y = 465
y = 155 kJ
Correct Answer: option <span>(1) Mn(s)
Reason:
The </span><span>spontaneity of electrochemical cell, depends on the it's Eo value. Electrochemical cells with positve Eo are spontanous and vice-versa.
</span>
In present case, the Eo of half-cell of interest are as follows:
Eo Zn2+/Zn = <span>-0.763v
</span>Eo Mg2+/Mg = 2.37v
Eo Mn2+/Mn = -1.18v
Therefore, Eo cell (with Zn as one of the half-cell) = Eo Zn2+/Zn - Eo Mn2+/Mn
= -0.763 - (-1.18)
= 0.417v
On other hand, Eo cell (with Mg as one of the half-cell) = Eo Mg2+/Zn - Eo Mn2+/Mn
= -2.37 - (-1.18)
= -1.19v
Thus, Mn(s) <span>metal will spontaneously react with Zn2+(aq), but will not spontaneously react with Mg2+(aq)</span>
For that you have to use the Aufbau principle
For example, writing the electronic configuration of Fe(28)
I recommend that you memorize the aufbau principle. Once you learn it, you don’t need anything else except the atomic number of the element to write it’s electronic configuration.