Changes in matter? How can it be?
Physical Changes • A physical change does not affect the nature or the characteristic properties of matter • Properties are retained • Examples: • Phase change • Dissolution • Deformation
Chemical Change • A chemical change changes the nature and characteristic properties of matter • Properties are not retained • Molecules are broken down and new ones are formed • Chemical changes can also be called reactions • Examples: • Synthesis • Decomposition • Precipitation • Combustion • Oxidation
Signs of a Chemical Change • The release of a gas • The release or absorption of heat • The emission of light • A change in color • The formation of a precipitate
Warning! • The release of a gas • The release or absorption of heat • The emission of light • A change in color • The formation of a precipitate PHYSICAL CHANGES CAN SOMETIMES SHOW THESE SIGNS AS WELL
Types of Chemical Reactions • Acid-Base Neutralization • Synthesis • Decomposition • Combustion • Precipitation
Which of the following reactions is an acid-base neutralization? 2 Na(s) + Cl2(g) 2 NaCl(s) 2 HI(aq) + Ba(OH)2 BaI2(aq) + 2 H2O(l) MgCl2(aq) + Na2SO3(aq) MgSO3(s) + 2 NaCl(aq)
Complete the following Acid-base Neutralizations • 2 HCl(aq) + Mg(OH)2(aq) • HNO3(aq) + KOH(aq) • HBr(aq) + NaOH(aq)
Synthesis and Decomposition • Synthesis: two or more reactants come together to form a new product. • Ex: N2(g) + 2O2(g) 2NO2(g) • Decomposition: A single reactant is broken up into two or more products. • 2H2O (l) 2H2 (g) + O2(g)
Single and Double Displacement Reactions • Single Displacement: A new compound is formed by the movement of one element or ion from one compound into a new one. • Double Displacement: Two ionic compounds switch cations(Positive ion).
Single or double? • AgNO3 + NaCl → AgCl + NaNO3 • 3 Mg (s) + 2 AlCl3 (aq) → 2 Al (s) + 3 MgCl2 (aq) • Pb(NO3)2(aq) + 2KCl (aq) → 2KNO3(aq) + PbCl2 (s)
Oxidation • Chemical reactions involving oxygen or a substance with similar properties. • Which other elements could act similarly to Oxygen?
Examples of Oxidation What is wrong here?
Combustion: A type of Oxidation • This type of chemical reaction involves the release of a large amount of energy. The Oxidizing Agent The Ignition Temperature The Substance to be burnt (will release a lot of energy in the presence of oxygen)
Types of Comubstion • Rapid Combustion: Within a short period of time, a lot of energy is released. (Light and heat energy, ex: fire) • Spontaneous Combustion: A rapid combustion in which the fuel reaches its ignition temperature without energy from an outside source. (No need to light the fuel) • Slow Combustion: A slow oxidation reaction such as decomposition, rusting, cellular respiration, etc.
Precipitation • A reaction in which a solid precipitate is formed from two non-solid reactants. • Ex: NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)
Your task (submitted on a loose leaf): • Last week in the lab, you carried various chemical and physical changes. • Heating and cooling of iodine • Mixing of iron and sulfur • Burning of iron and sulfur • Mixing of NaOH and CaCl2 • Mixing of HCl and CaCO3 (marble chips) • You must determine whether you observed a chemical or a physical change. • For each of the chemical changes observed you must: • Provide evidence for how you determined that this was a chemical change (signs). • Identify the type of chemical change that you observed (when possible). • A balanced chemical equation for each of the reactions you carried out.