The element first discovered in the sun is the element Helium. This noble gas is the second most abundant element<span> in the universe and was </span>discovered<span> on the </span>sun<span> before it was discovered on the earth. Helium is the result of the nuclear fusion of hydrogen creating thus the mass of energy in the sun.</span>
Answer:
again same questions
i think its from 1st chapter
<span>Quarks are present in protons and neutrons but not in electrons.</span>
Answer : The enthalpy change of reaction is -23.9 kJ
Explanation :
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 given final reaction is,

The intermediate balanced chemical reaction will be,
(1)

(2)

First we will reverse the reaction 1 and multiply equation 2 by 3 then adding both the equation, we get :
(1)

(2)

The expression for final enthalpy is,



Therefore, the enthalpy change of reaction is -23.9 kJ