ECAT MCQs

Chemical reactions rearrange atoms but do not create or destroy them.
Therefore total mass remains constant in a closed system.

A pure compound has constant composition.
This is also called the law of constant composition.

Molar mass is numerically related to relative atomic or molecular mass.
Its common unit is g/mol.

An empirical formula shows the lowest integer ratio of elements.
It may differ from the molecular formula.

A molecular formula is a whole-number multiple of the empirical formula.
It applies to substances composed of discrete molecules.

Balancing follows conservation of atoms and mass.
Coefficients change amounts, not chemical formulas.

Chemistry examines what matter is made of and how it behaves.
It also studies energy changes accompanying chemical processes.

Equation coefficients give stoichiometric ratios.
They may be interpreted as molecule or mole ratios.

Matter includes solids, liquids, gases, and plasma.
It is composed of atoms, molecules, or ions.

Once the limiting reactant is used up, no more product can form.
Other reactants may remain in excess.

An element cannot be broken down chemically into simpler substances.
Each element is identified by its atomic number.

An excess reactant is supplied beyond the stoichiometric requirement.
Some remains when the reaction is complete.