A. reduce the need to use fossil fuels
Answer : The enthalpy change of reaction is -1800 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 multiply reaction 1 by 2 and reverse reaction of reaction 2 by 3 then adding both the equation, we get :
The expression for final enthalpy is,
![\Delta H=[n\times \Delta H_1]+[n\times (-\Delta H_2)]](https://tex.z-dn.net/?f=%5CDelta%20H%3D%5Bn%5Ctimes%20%5CDelta%20H_1%5D%2B%5Bn%5Ctimes%20%28-%5CDelta%20H_2%29%5D)
where,
n = number of moles
![\Delta H=[2mole\times (-1680kJ/mole)]+[3\times -(-520kJ/mole)]](https://tex.z-dn.net/?f=%5CDelta%20H%3D%5B2mole%5Ctimes%20%28-1680kJ%2Fmole%29%5D%2B%5B3%5Ctimes%20-%28-520kJ%2Fmole%29%5D)

Therefore, the enthalpy change of reaction is -1800 kJ
I believe it is less dense.. that is why ice floats on water
Answer:
1.48 moles of SeCl6 are needed
Explanation:
Based on the reaction:
SeCl6 + O2 → SeO2 + 3Cl2
<em>1 mole of SeCl6 reacts producing 3 moles of Cl2.</em>
To solve this question we need to use the conversion factor:
1mol SeCl6 = 3mol Cl2
As we want to produce 4.45 moles of Cl2, we need:
4.45 mol Cl2 * (1mol SeCl6 / 3mol Cl2) =
<h3>1.48 moles of SeCl6 are needed</h3>