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A synthesis reaction is a type of reaction in which multiple reactants combine to form a single product. Synthesisreactions release energy in the form of heat and light, so they are exothermic. An example of a synthesis reaction is the magnesium and oxygen which gives a white powder of the magnesium oxide.
The equation involved in the reaction can be summarised as;
2Mg(s) + O2(g) = 2MgO(s) + energy.........
The gain in mass 96.289g-93.000g=3.289g , was as a result of magnesium combinaing with oxygen in the air.
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