13. For the following reaction, use Hess's law to calculate AGʻrxn given the information below. Reaction: CO(g) + C(s) + 1/2 O2(g)
Gºrxn = ?
Given: CO2(g) → C(s) + O2(g)
CO(g) + 1/2 O2(g) + CO2(g)
AGʻrxn = +394.4 kJ
AGºrxn = -257.2 kJ

you need to give more information

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)