4.1 Introduction to Reactions + 4.4 Physical and Chemical Changes

When does a physical change occur?

When a substance undergoes a change in properties but not a change in composition

What are common physical changes?

Changes in phase of a substance or formation/separation of mixtures of substances

When does a chemical change occur?

When substances are transformed into new substances with different compositions

What provides possible evidence that a chemical change has occurred?

Production of heat or light, formation of a gas, formation of a precipitate, color change

What processes are classified as chemical processes?

Processes that involve the breaking and/or formation of chemical bonds

What processes are classified as physical processes?

Processes that involve only changes in intermolecular interactions

Example of processes that involve only changes in intermolecular interactions:

Phase changes

Can physical processes involve the breaking of chemical bonds?

Yes

Example of physical processes involving the breaking of chemical bonds:

Dissolution of salt in water involves the breaking of ionic bonds

Is dissolution of salt in water a physical or chemical process?

Both

Why is dissolution of salt in water both a physical and chemical process?

It involves the breaking of ionic bonds and the formation of ion-dipole interactions between ions and solvent

Examples of property changes that indicate a physical process?

Particle size, texture, shape

When does a change of phase occur?

When a pure substance is heated or cooled

How are mixtures separated into simpler substances?

Through distillation, chromatography, or filtration

Production of heat or light is evidence of what?

Change in energy

Production of odor is an indicator of what?

Chemical change

Why is production of odor an indicator of a chemical change?

It is associated with the formation of a new gaseous substance

Is a change in color an indicator of a chemical change?

Not necessarily

Example of a color change that is not an indicator of a chemical change:

Mixing a sample of blue dye and yellow dye produces a new green color

Is mixing dyes a physical or chemical change?

Physical

Why is mixing dyes a physical change?

Only a mixture is formed and the dyes do not change in chemical composition

Example of a color change that indicates a chemical change:

Acid-base indicator changes color

Why is the change in color of an acid-base indicator an indicator of a chemical change?

It changes color as a result of a change in its chemical structure

What happens at the particle level during a phase change?

Attractive forces between molecules of a pure substance are broken or formed

What happens at the particle level during the separation or formation of a mixture?

Attractive forces between particles of solute and solvent are broken or formed

What happens at the particle level during a chemical change?

Chemical bonds are broken or formed to produce new chemical compositions