Conservation of Mass & Balanced Chemical Equations

What does the Law of Conservation of Mass state?

No matter is lost or gained during a chemical reaction.

What must be true about the total mass of reactants and products in a chemical reaction?

The total mass of the reactants is equal to the total mass of the products.

What is a precipitation reaction?

A reaction in which two solutions react to form an insoluble solid called a precipitate.

What happens to the mass of a closed reaction flask during a reaction?

The total mass remains constant.

What is the balanced equation for the reaction between calcium chloride and sodium sulfate?

CaCl2 (aq) + Na2SO4 (aq) ⟶ CaSO4 (s) + 2NaCl (aq)

What occurs to the mass of a reaction flask if a gaseous product escapes?

The total mass of the reaction flask will change as product mass is lost.

What is the balanced equation for the reaction between hydrochloric acid and calcium carbonate?

2HCl (aq) + CaCO3 (s) ⟶ CaCl2 (aq) + H2O (l) + CO2 (g)

What is the implication of matter not being created or destroyed in a chemical reaction?

The total amount of matter before and after a reaction is the same.

What does a subscript number in a chemical formula indicate?

The number of atoms of the element just before it.

What does a subscript number after brackets in a chemical formula apply to?

It applies to all of the elements inside the bracket.

What is the significance of balancing chemical equations?

There must be the same number of atoms of each element on either side of the equation.

Which non-metals must be written as molecules in chemical equations?

H2, N2, O2, F2, Cl2, Br2, and I2.

What is the recommended approach for balancing chemical equations?

Practice lots of examples and adjust coefficients one by one.

In the equation 2Fe2O3, what does the large number before the chemical indicate?

It applies to the entire chemical, indicating there are four iron atoms and six oxygen atoms.

What is the purpose of using coefficients in a chemical equation?

To indicate the number of molecules or moles of each substance involved in the reaction.

What is the result of a balanced acid-base neutralization reaction?

NaOH (aq) + HCl (aq) ⟶ NaCl (aq) + H2O (l)

What is a redox reaction?

A reaction that involves the transfer of electrons between substances.

What is the role of relative atomic/molecular masses in chemical reactions?

They must be the same for both reactants and products in a balanced equation.

What happens if the mass of a reaction flask increases during a reaction?

It may be due to a gaseous reactant from the air being involved.

What is the first step in balancing a chemical equation?

Work across the equation from left to right, checking one element after another.

What should you do if a group of atoms remains unchanged during a reaction?

Count the whole group as one entity rather than individual atoms.