General Chemistry Concepts

What is the sign of work when a gas expands?

Work is negative because the system does work on the surroundings.

What is the sign of work when a gas is compressed?

Work is positive because the surroundings do work on the system.

What is a precipitation reaction?

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

When is ΔH°f = 0?

For an element in its standard state at 25°C and 1 atm.

What does an oxidation state tell you?

It represents the apparent charge an atom would have if bonding electrons were assigned to the more electronegative atom.

What is the equation for the First Law of Thermodynamics?

ΔE = q + w

What does q > 0 mean?

The system absorbs heat from the surroundings.

What does q < 0 mean?

The system releases heat to the surroundings.

What is the difference between a strong and weak acid?

A strong acid completely ionizes in water; a weak acid only partially ionizes.

What is a strong electrolyte?

A substance that completely dissociates or ionizes in aqueous solution and produces many ions.

What is a weak electrolyte?

A substance that partially ionizes in water, producing fewer ions.

What makes a molecule polar?

It has an unequal distribution of charge and usually has a net dipole.

What makes a molecule nonpolar?

Its bond dipoles cancel, resulting in no net dipole.

What does it mean if a reaction is reactant-favored?

At equilibrium, there are more reactants than products.

What does it mean if a reaction is product-favored?

At equilibrium, there are more products than reactants.

What is oxidation?

Loss of electrons. OIL = Oxidation Is Loss.

What is reduction?

Gain of electrons. RIG = Reduction Is Gain.

What is an indicator in a titration?

A chemical that changes color near the endpoint of a titration.

What is a colorimeter?

An instrument that measures light absorbance/transmission of a solution.

What happens during an exothermic reaction?

The system releases heat, the surroundings usually warm, and ΔH is negative.

What happens during an endothermic reaction?

The system absorbs heat, the surroundings usually cool, and ΔH is positive.

When does ΔH = qₚ?

At constant pressure, assuming only pressure-volume work occurs.

What is the relationship between pH and pOH?

pH + pOH = 14 at 25°C.

What does ΔG < 0 mean?

The process is spontaneous under the given conditions.

How does heat capacity affect temperature change?

For the same amount of heat, a higher heat capacity causes a smaller ΔT, while a lower heat capacity causes a larger ΔT.