Question

how does the law of conservation of mass apply to this reaction: $c_{2}h_{4}+o_{2}\to2h_{2}o + 2co_{2}$?
only the oxygen needs to be balanced. there are equal numbers of hydrogen and carbon
the law of conservation of mass has already been applied. there is an equal number of each element on both sides of the equation.
the equation needs to be balanced. there are fewer oxygen atoms in the equation than hydrogen or carbon.
each element needs to be balanced.

Explanation:

Step1: Count atoms on each side

• Reactants:
• \(C_2H_4\): \(2\) carbon (\(C\)) atoms and \(4\) hydrogen (\(H\)) atoms.
• \(O_2\): \(2\) oxygen (\(O\)) atoms.
• Products:
• \(2H_2O\): \(4\) hydrogen (\(H\)) atoms and \(2\) oxygen (\(O\)) atoms.
• \(2CO_2\): \(2\) carbon (\(C\)) atoms and \(4\) oxygen (\(O\)) atoms.
• Total oxygen in products: \(2 + 4=6\) atoms.

Step2: Analyze balance

• Carbon (\(C\)): \(2\) atoms on both sides (balanced).
• Hydrogen (\(H\)): \(4\) atoms on both sides (balanced).
• Oxygen (\(O\)): \(2\) atoms on reactant side vs. \(6\) atoms on product side (not balanced). So the equation needs balancing.

Answer:

C. The equation needs to be balanced. There are fewer oxygen atoms in the equation than hydrogen or carbon.