Question

which represents a balanced chemical equation? *
2 point
○ co₂ + h₂o → ch₄ + o₂
○ ch₄ + o₂ → co₂ + h₂o
○ ch₄ + 2o₂ → co₂ + 2h₂o
○ co₂ + 2h₂o → 2ch₄ + 2o₂

which law explains why chemical reactions must be balanced? *
2 point
○ multiple properties
○ conservation of mass
○ conservation of energy
○ gravity

which equation represents a synthesis chemical reaction? *
2 point
○ 2s + 3o₂ → 2so₃
○ 2k + 2h₂o → 2koh + h₂
○ 2nacl → 2na + cl₂
○ zn + 2hcl → zncl₂ + h₂

Explanation:

First Question (Balanced Chemical Equation)

Step1: Analyze first option

For \( \ce{CO2 + H2O -> CH4 + O2} \), count atoms: C:1→1, O:3→2, H:2→4. Not balanced.

Step2: Analyze second option

For \( \ce{CH4 + O2 -> CO2 + H2O} \), count atoms: C:1→1, O:2→3, H:4→2. Not balanced.

Step3: Analyze third option

For \( \ce{CH4 + 2O2 -> CO2 + 2H2O} \), count atoms: C:1→1, O:4→4, H:4→4. Balanced.

Step4: Analyze fourth option

For \( \ce{CO2 + 2H2O -> 2CH4 + 2O2} \), count atoms: C:1→2, O:4→4, H:4→8. Not balanced.

The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. Thus, the number of atoms of each element must be equal on both sides of a chemical equation, requiring it to be balanced. "Multiple Properties" is not a relevant law, "Conservation of Energy" relates to energy, and "Gravity" is a force, not related to chemical reaction balancing.

Step1: Recall synthesis reaction

A synthesis reaction is when two or more substances combine to form a single product (\( A + B
ightarrow AB \)).

Step2: Analyze first option

\( \ce{2S + 3O2 -> 2SO3} \): S and \( O_2 \) combine to form \( SO_3 \) (synthesis).

Step3: Analyze second option

\( \ce{2K + 2H2O -> 2KOH + H2} \): Single - displacement (K displaces H in \( H_2O \)).

Step4: Analyze third option

\( \ce{2NaCl -> 2Na + Cl2} \): Decomposition (compound breaks into elements).

Step5: Analyze fourth option

\( \ce{Zn + 2HCl -> ZnCl2 + H2} \): Single - displacement (Zn displaces H in HCl).

Answer:

C. \( \ce{CH4 + 2O2 -> CO2 + 2H2O} \)

Second Question (Law for Balanced Reactions)