Changes in Matter Matter Lecture 2
Physical Properties Characteristic Examples: Observed or measured Doesn’t change the makeup of the substance Examples: Color, odor, taste, hardness, density, melting point, boiling point People are used to identifying something based on its properties…
Physical properties of metals Ductile: can be drawn into a wire Malleable: can be hammered into sheets Luster: shine Good conductor of heat and electricity
Density Ratio of mass to volume Density = mass / volume Common units of density: kg/m3, g/cm3, g/mL Practice Problem: A piece of lead has a mass of 22.7 g. It occupies a volume of 2.0 cm3. What is the density of the lead? D= 22.7/2= 11.4 g/cm3
Practice Problem 2 A piece of lead occupies a volume of 4.0 cm3. What is the mass of the lead if density is 11.4 g/cm3?
Practice Problem 3 A piece of lead (density 11.4 g/cm3) has a mass of 302 g. What volume does it occupy?
Physical Change No new substance is formed Examples: Change of color (with no change in composition) Grinding of substances into powders
Change of phase/state (solid, liquid, gas) Dependent on temperature and pressure
Phase Changes
Chemical Properties Properties that describe how the substance interacts (or fails to interact) with other substances to produce new substances Example: Rust combustion
Chemical Change Process that involves one or more substances forming something new Always produces a change in properties Examples: Rusting of iron Souring of milk Burning of paper
Chemical Reaction Chemical changes are chemical reactions Reactants products
Law of Conservation of Mass Matter cannot be created or destroyed True for all chemical and physical changes Massreactants = Massproducts Example: If 11.2 g of hydrogen and 88.8 g of oxygen react to form water, how much water will be formed?
Both chemical and physical changes involve changes in energy… Endothermic Absorbs energy Examples: Melting ice Water absorbs energy to break down into oxygen and hydrogen gas Exothermic Releases energy Burning paper Freezing water