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