ECAT Chemistry MCQs

At equilibrium there is no net driving force for change.
The reaction mixture has minimum Gibbs energy under the conditions.

A closed system has fixed mass.
Heat or work may still cross its boundary.

At equilibrium, concentrations remain constant over time.
Molecules continue reacting in both directions.

An ideal isolated system has no interaction with surroundings.
A perfect thermos is an approximate example.

The equilibrium expression follows stoichiometric powers.
Its value depends on temperature.

Internal energy includes molecular motion, bonding, and interactions.
Only changes in internal energy are directly measured.

A large K means the equilibrium mixture contains mostly products.
It does not directly indicate reaction speed.

Enthalpy is H=U+PV.
At constant pressure, enthalpy change equals heat transferred for PV work.

A small K means little product is present at equilibrium.
The forward reaction may still occur.

Exothermic processes have negative enthalpy change under the usual convention.
The surroundings gain heat.

Endothermic processes have positive enthalpy change.
The system gains heat.

Heat capacity depends on the amount and identity of matter.
Specific heat capacity is heat capacity per unit mass.