Question

phet online lab, balancing chemical equations
in this online lab you will use the laws of conservation of mass to: (1) balance chemical
chemical reactions, mass is never lost or gained. the mass of the reactants must be equal to the mass of the
products. in other words, in every chemical reaction there must be the same number of atoms of
each element on each side of the chemical equation. answer the questions below before you begin
using the simulation.
ch4 + 2o2 → co2 + 2h2o
(1) above is the balanced chemical equation for the reaction of methane (ch4) and oxygen
gas (o2) to produce carbon dioxide (co2) and water (h2o). using this chemical formula,
answer the following questions.
a) what are the elements and compounds on the left side of the equation called?
________________________
b) what are the elements and compounds on the right side of the equation called?
________________________
c) what does the 4 after the h in the chemical formula for methane tell you?
________________________
d) what does the 2 in front of the chemical formula for water tell you?
________________________
e) what do we call the numbers that are placed in front of a molecules chemical formula?
________________________
f) what do we call the smaller numbers that appear after or between the element symbols in a
chemical formula?
________________________

Explanation:

• a) In a chemical equation, the substances on the left - hand side of the arrow are called reactants. Here, \(CH_4\) (methane, a compound) and \(O_2\) (oxygen gas, an element) are the reactants.
• b) The substances on the right - hand side of the arrow are called products. \(CO_2\) (carbon dioxide, a compound) and \(H_2O\) (water, a compound) are the products.
• c) In the formula \(CH_4\), the subscript \(4\) after \(H\) indicates that there are 4 hydrogen atoms in one molecule of methane.
• d) The \(2\) in front of \(H_2O\) (i.e., \(2H_2O\)) is a coefficient. It means there are 2 molecules of water.
• e) The numbers placed in front of a molecule's chemical formula (like the \(2\) in \(2O_2\) and \(2H_2O\)) are called coefficients.
• f) The smaller numbers that appear after or between the element symbols in a chemical formula (like the \(4\) in \(CH_4\) and the \(2\) in \(H_2O\) and \(CO_2\)) are called subscripts.

Answer:

a) Reactants: \(CH_4\) (compound) and \(O_2\) (element).
b) Products: \(CO_2\) (compound) and \(H_2O\) (compound).
c) There are 4 hydrogen atoms in one molecule of methane.
d) There are 2 molecules of water.
e) Coefficients.
f) Subscripts.