The sum of the percentage abundance of these two isotopes of the new synthetic element should be equal to 100. If we let x be the percent abundance of the second isotope, we have the equation, 43 + x = 100The value of x = 57
Answer : The standard enthalpy of formation of methanol is, -238.7 kJ/mole
Explanation :
Standard formation of reaction : It is a chemical reaction that forms one mole of a substance from its constituent elements in their standard states.
According to Hess’s law of constant heat summation, the heat absorbed or evolved in a given chemical equation is the same whether the process occurs in one step or several steps.
According to this law, the chemical equation can be treated as ordinary algebraic expression and can be added or subtracted to yield the required equation. That means the enthalpy change of the overall reaction is the sum of the enthalpy changes of the intermediate reactions.
The formation reaction of
will be,

The intermediate balanced chemical reaction will be,
(1)

(2)

(3)

Now we will reverse the reaction 3, multiply reaction 2 by 2 then adding all the equations, we get :
(1)

(2)

(3)

The expression for enthalpy of formation of
will be,



Therefore, the standard enthalpy of formation of methanol is, -238.7 kJ/mole
I’m not too sure because i forgot about this but i thik it’s D, good luck
Balanced chemical equation is :

It is given that the equation is in equilibrium.
We need to find what will happen if we add more
is added .
By Le Chatelier's principle :
Changing the concentration of a chemical will shift the equilibrium to the side that would counter that change in concentration.
It means production of the side where content is added will decrease and concentration on other side will increase .
So , more NO would form .
Therefore, option B. is correct.
Hence, this is the required solution.
One box is 120g.
mass of 126 boxes = 126*120 = 15120 g
(note: used an additional significant figure when first digit is a 1, so four significant figures)
Using the conversion 1 lb. = 453.6 g/lb
15120g = 15120 g / (453.6 g/lb) = 15120 g * (1/453.6) lb/g = 33.3 lbs. (3 significant figures)