Time taken for star to reach Earth = 7.5 years
<h3>Further explanation</h3>
Given
7.5 light years(distance Earth-star)
Required
Time taken
Solution
Speed of light=v = 3 x 10⁸ m/s
1 light years = 9.461 × 10¹⁵ m= distance(d)
So time taken for 1 light years :
time(t) = distance(d) : speed(v)
t = 9.461 × 10¹⁵ m : 3 x 10⁸ m/s
t = 3.154 x 10⁷ s = 1 years
So for 7.5 light years, time taken = 7.5 years
Water, Water is not a pure substance. It is a mixture, and Chromatography
<span>Ka is an equilibrium constant for the partial ionization of "weak" acids in water.</span>
<u>Answer:</u> The enthalpy of the reaction is coming out to be -902 kJ.
<u>Explanation:</u>
Enthalpy change is defined as the difference in enthalpies of all the product and the reactants each multiplied with their respective number of moles. It is represented as 
The equation used to calculate enthalpy change is of a reaction is:
![\Delta H_{rxn}=\sum [n\times \Delta H_f_{(product)}]-\sum [n\times \Delta H_f_{(reactant)}]](https://tex.z-dn.net/?f=%5CDelta%20H_%7Brxn%7D%3D%5Csum%20%5Bn%5Ctimes%20%5CDelta%20H_f_%7B%28product%29%7D%5D-%5Csum%20%5Bn%5Ctimes%20%5CDelta%20H_f_%7B%28reactant%29%7D%5D)
For the given chemical reaction:

The equation for the enthalpy change of the above reaction is:
![\Delta H_{rxn}=[(4\times \Delta H_f_{(NO(g))})+(6\times \Delta H_f_{(H_2O(g))})]-[(4\times \Delta H_f_{(NH_3(g))})+(5\times \Delta H_f_{(O_2)})]](https://tex.z-dn.net/?f=%5CDelta%20H_%7Brxn%7D%3D%5B%284%5Ctimes%20%5CDelta%20H_f_%7B%28NO%28g%29%29%7D%29%2B%286%5Ctimes%20%5CDelta%20H_f_%7B%28H_2O%28g%29%29%7D%29%5D-%5B%284%5Ctimes%20%5CDelta%20H_f_%7B%28NH_3%28g%29%29%7D%29%2B%285%5Ctimes%20%5CDelta%20H_f_%7B%28O_2%29%7D%29%5D)
We are given:

Putting values in above equation, we get:
![\Delta H_{rxn}=[(4\times (91.3))+(6\times (-241.8))]-[(4\times (-45.9))+(5\times (0))]\\\\\Delta H_{rxn}=-902kJ](https://tex.z-dn.net/?f=%5CDelta%20H_%7Brxn%7D%3D%5B%284%5Ctimes%20%2891.3%29%29%2B%286%5Ctimes%20%28-241.8%29%29%5D-%5B%284%5Ctimes%20%28-45.9%29%29%2B%285%5Ctimes%20%280%29%29%5D%5C%5C%5C%5C%5CDelta%20H_%7Brxn%7D%3D-902kJ)
Hence, the enthalpy of the reaction is coming out to be -902 kJ.