Answer:
In a chemical equation, chemicals that react are the reactants, while chemicals that are produced are the products/by products. Both sides of the equation must be balanced.
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Explanation
When writing a chemical equation, reactants reacts to produce products. For example in the equation for formation of water, hydrogen combines with oxygen as 2H₂ +O₂→2H₂O where the first part before the arrow represent the reactants and the next part after the arrow are the products. Reactants are on the left where as products are on the right.Coefficient 2, in this cases is used for balancing the equation
It is energy associated with gravity or gravitational force. (Potential<span> </span>energy<span> held by an object because of its high position compared to a lower position).</span>
Answer: -
100 grams
Explanation: -
Mass of Oxygen = 40 g
Chemical formula of oxygen gas = O2
Molar mass of oxygen = 16 x 2 = 32 gram
Atomic mass of Mg = 24g
Molar mass of MgO = 24 x 1 + 16 x 1 =40 gram
The balanced chemical equation for the reaction is
2Mg + O2 -- > 2 MgO
So from the balanced equation we see that 1 O2 react to give 2 MgO
32 grams of O2 react to give 2 x 40 gram of MgO
40 grams of O2 react to give 
=100 gram of MgO
