I´m pretty sure its magnesium iron silicate.
Hello.
The answer is <span>+313.766 J/mol·K
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Use the coefficients of the reaction and sum the product entropies less the reactant entropies:
4*188.8 + 2*213.7 - 3*205.1 - 2* 126.8 = 313.7 J/mol*K
Have a nice day