PIEAS Pre Engineering MCQs

Stoichiometry uses balanced equations to relate amounts.
It supports mass, mole, particle, and gas calculations.

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

Theoretical yield assumes complete reaction and no losses.
It is calculated from the limiting reactant.

Actual yield is measured after the experiment.
It is usually lower than theoretical yield.

Percent yield measures reaction and recovery efficiency.
Values below 100% commonly result from losses or incomplete reaction.

Molarity is a common concentration unit.
Its value changes with temperature because solution volume can change.

Molality is based on solvent mass.
It is largely independent of temperature.

Mass percent expresses composition on a mass basis.
All component mass percentages sum to 100%.

Mole ratios convert amounts of one substance into another.
They come directly from the balanced equation.

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.

Percent composition is calculated from formula mass contributions.
The element percentages sum to approximately 100%.