<h3>The average atomic mass of Iodine : 126.86 amu</h3><h3>Further explanation</h3>
Given
80% 127I, 17% 126I, and 3% 128I.
Required
The average atomic mass
Solution
The elements in nature have several types of isotopes
Atomic mass is the average atomic mass of all its isotopes
Mass atom X = mass isotope 1 . % + mass isotope 2.% + ... mass isotope n.%
Atomic mass of Iodine = 0.8 x 127 + 0.17 x 126 + 0.03 x 128
Atomic mass of Iodine = 101.6 + 21.42 + 3.84
Atomic mass of Iodine = 126.86 amu
Answer: The value of 
for the reaction is, -2512.4 kJ
Explanation:
The chemical equation for the combustion of acetylene follows:
The equation for the enthalpy change of the above reaction is:
![\Delta H^o_{rxn}=[(3\times \Delta H^o_f_{(CO_2(g))})+(4\times \Delta H^o_f_{(H_2O(g))})]-[(1\times \Delta H^o_f_{(C_2H_2(g))})+(5\times \Delta H^o_f_{(O_2(g))})]](https://tex.z-dn.net/?f=%5CDelta%20H%5Eo_%7Brxn%7D%3D%5B%283%5Ctimes%20%5CDelta%20H%5Eo_f_%7B%28CO_2%28g%29%29%7D%29%2B%284%5Ctimes%20%5CDelta%20H%5Eo_f_%7B%28H_2O%28g%29%29%7D%29%5D-%5B%281%5Ctimes%20%5CDelta%20H%5Eo_f_%7B%28C_2H_2%28g%29%29%7D%29%2B%285%5Ctimes%20%5CDelta%20H%5Eo_f_%7B%28O_2%28g%29%29%7D%29%5D)
We are given:
Putting values in above equation, we get:
![\Delta H^o_{rxn}=[(4\times (-393.5))+(2\times (-241.8))]-[(2\times (227.4)+(5\times (0))]\\\\\Delta H^o_{rxn}=-2512.4kJ](https://tex.z-dn.net/?f=%5CDelta%20H%5Eo_%7Brxn%7D%3D%5B%284%5Ctimes%20%28-393.5%29%29%2B%282%5Ctimes%20%28-241.8%29%29%5D-%5B%282%5Ctimes%20%28227.4%29%2B%285%5Ctimes%20%280%29%29%5D%5C%5C%5C%5C%5CDelta%20H%5Eo_%7Brxn%7D%3D-2512.4kJ)
Therefore, the value of for the reaction is, -2512.4 kJ
The ionic equation is as below
Ca^2+(aq) + SO4^2-(aq) ---> CaSO4(s)
EXPLANATION
K2SO4(aq) +Cai2(aq) ---> CaSO4(s) + Ki (aq)
ionic equation
= 2K^+(aq) + SO4^2-(aq) + Ca^2+(aq) + 2i^-(aq) --->CaSO4(s) + 2K^+(aq) +2 i^-(aq)
cancel the spectator ions that is 2k^+ and 2i^-
The net ionic equation is therefore
= Ca^2+(aq) + SO4^2-(aq) ----> CaSO4(s)
