Final answer:
A chemical equation is balanced when the number of atoms of each element is equal on both the reactant and product sides. For the equations provided, some are balanced, like CH4 + 2O2 → CO2 + 2H2O, while others need coefficients adjusted, such as Na and O2 → Na2O.
Step-by-step explanation:
To determine if a chemical equation is balanced, the number of atoms for each element must be equal on both the reactant and product sides of the equation. Evaluating the provided reactions:
For 2Na(s) + O₂(g) → 2Na₂O(s), the equation is not balanced because there are different numbers of sodium and oxygen atoms on each side.
CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l) is balanced, as there are equal numbers of carbon, hydrogen, and oxygen atoms on both sides.
AgNO₃(aq) + 2KCl(aq) → AgCl(s) + KNO₃(aq) is also balanced, with conservation of silver, nitrogen, chlorine, and potassium atoms.
2Hg + O₂ → Hg₂O₂ is balanced because there is an equal number of mercury and oxygen atoms on both sides.
C₂H₄(g) + 2O₂(g) → 2CO₂(g) + 2H₂O(l) is balanced with the correct number of carbon, hydrogen, and oxygen atoms.
Mg(NO₃)₂(s) + 2Li(s) → Mg(s) + 2LiNO₃(s) is balanced, ensuring that magnesium, nitrogen, lithium, and oxygen atoms are conserved.
For balancing equations, such as N₂(g) + O₂(g) → NO₂(g), the approach involves ensuring that the number of nitrogen and oxygen atoms are equal on both sides by adjusting the coefficients appropriately.
The reaction of Na and Cl₂ becoming 2 NaCl is explained as straightforward to balance by inspection. This involves changing coefficients to ensure equal numbers of each type of atom on both sides of the reaction.