Physical vs. Chemical Properties

Part 1 The study of matter

NC Essential Standards

• 8.P.1 Understand the properties of matter and changes that occur when matter interacts in an open and closed container – 8.P.1.1: Classify matter as elements, compounds, or mixtures based on how the atoms are packed together in arrangements – 8.P.1.2: Explain how the physical properties of elements and their reactivity have been used to produce the current model of the Periodic Table of Elements – 8.P.1.3 Compare physical changes such as size, shape and state to chemical changes that are the result of a chemical reaction to include changes in temperature, color, and formation of a gas or precipitate.

– 8.P.1.4: Explain how the idea of atoms and a balanced chemical equation support the law of conservation of mass.

Reviewing MATTER

• Matter: anything that has mass and takes up space – Mass – the amount of matter in something – Volume – the amount of space something occupies • Which of the following is matter?

– A car?

– A box?

– You?

What is a property?

• Property: a characteristic of a substance that can be observed

Physical Property

Physical property: a property that can be observed without changing the identity of the substance.

Examples: • luster • malleability: the ability to be hammered into a thin sheet • ductility: the ability to be stretched into a wire • melting point • boiling point • density • solubility • specific heat

Special Physical Properties

• • Melting point: the temperature at which a substance changes from a solid to a liquid at a given pressure water = 0 o C Boiling point: the temperature at which a substance changes from a liquid to a gas at a given pressure water = 100 o C

Chemical Properties

• Chemical property: a property that can only be observed by changing the identity of the substance Examples: •flammability •ability to rust •reactivity with vinegar

Density

• Density is the amount of mass per unit of volume.

• Density can be used to identify a substance.

• The density of water is 1.0g/mL

Density Calculations

• • Calculations: D = m/V = g/mL = g/cm 3 Ex: A cube has a mass of 2.8 g and occupies a volume of 3.67 ml. Would this object float or sink in water?

Mass = 2.8 g Volume = 3.67 mL D = 2.8g/3.67 mL= 0.76 g/mL – This object would float in water because its density is less than water (1.0 g/mL).

More Density Calculations

• Ex: A liquid has a mass of 25.6 g and a volume of 31.6 mL. Use the table below to identify the substance.

M=25.6 g V=31.6 mL D = 25.6 g/31.6 mL D= 0.81 g/mL The substance is ethanol.

Substance Mercury Water Ethanol Density (g/mL) 13.6 1.00 0.81

Physical vs. Chemical Changes

Part 2

Concept of Change

• • Change: the act of altering a substance Change of state/phase – Solid, Liquid, Gas

Physical Change

• – – – Physical change: a change that occurs that does not change the identity of the substance – Melting ice Freezing Kool-aid Tearing paper Boiling water

Chemical Changes

• • Chemical change: a change that occurs causing the identity of the substance to change – Burning – – Digesting food Reacting with other substances A chemical change is called a chemical

reaction

Chemical Changes Cont’d

• Indicators of a chemical change: • Evolution of light • • • • Evolution of heat Evolution of a gas Color change Formation of a precipitate

Is it Physical or Chemical?

Change

Melting cheese Burning wood Milk souring Wadding up paper Bicycle rusting

Physical Chemical