Stoichiometric Relationships 1.1 - Introduction to the Particulate Nature of Matter & Chemical Change

Essential Idea Physical and chemical properties depend on the ways in which different atoms combine. NATURE OF SCIENCE (3.1) Making quantitative measurements with replicates to ensure reliability – definite and multiple proportions.

International-Mindedness Chemical symbols and equations are international, enabling effective communication amongst scientists without need for translation. IUPAC (International Union of Pure and Applied Chemistry) is the world authority in developing standardized nomenclature for both organic and inorganic compounds,

Theory of Knowledge Chemical equations are the “language” of chemistry. How does the use of universal languages help and hinder the pursuit of knowledge? Lavoisier’s discovery of oxygen, which overturned the phlogiston theory of combustion, is an example of a paradigm shift. How does scientific knowledge progress?

Pure Substances occur naturally, same composition throughout the substance, and same composition everywhere in the world

Chemistry Chemistry is the study of matter (what things are made up of), its properties, and the changes that they undergo.

Have a specific or definite composition Pure Substances MATTER (Pure) Substances Elements Compounds Anything that has mass and takes up space Have a specific or definite composition (homogeneous) Examples: iron sulfur, carbon, Hydrogen, oxygen Examples: water, salt, sugar

Elements Elements: The simplest form of matter Cannot be broken down or separated into a simpler substance Building blocks for all other substances Found on the periodic table of elements

Understanding 1.1.A Atoms of different elements combine in fixed ratios to form compounds, which have different properties from their component elements.

Compounds Compounds: Chemical combination of 2 or more substances Cannot be physically separated Have properties different than the elements that are combined

Understanding 1.1.B Mixtures contain more than one element and/or compound that are not chemically bonded together and so retain their individual properties.

Physical combinations of two or more substances Mixtures MATTER Mixtures Homogeneous Heterogeneous Anything that has mass and takes up space Physical combinations of two or more substances Uniform throughout, aka “solution”; Think: smoothie Not uniform throughout, distinct pieces; Think: fruit salad

Understanding 1.1.C Mixtures are either homogeneous or heterogeneous.

Matter MATTER (Pure) Substances Mixtures Homogeneous Heterogeneous Anything that has mass and takes up space Physical combinations of two or more substances Uniform throughout, aka “solution”; Think: smoothie Not uniform throughout, distinct pieces; Think: fruit salad (Pure) Substances Elements Compounds Have a specific or definite composition (homogeneous) Examples: iron sulfur, carbon, Hydrogen, oxygen Examples: water, salt, sugar

Application/Skills Be able to explain the observable changes in physical properties and temperature during changes of state.

Heating/Cooling Curve

Application/Skills Be able to name the changes of state: – melting, – freezing, – vaporization (evaporation and boiling), – condensation, – sublimation, and – deposition SI unit for temperature is the kelvin (K) K = °C + 273°

Application/Skills Be able to apply the state symbols (s), (l), (g) and (aq) in equations.

2H2(g) + O2(g) → 2H2O(l) The states of substances are indicated in parenthesis next to the formula. Solid (s) Liquid (l) Gas (g) Aqueous solution (aq) – indicates that the ions are dissolved in water. A single arrow means the rxn essentially goes to completion. A double arrow means equilibrium.

Application/Skills Be able to deduce chemical equations when reactants and products are specified.

Law of Conservation of Matter Atoms cannot be created or destroyed in a chemical reaction, they can only be rearranged. The reactants (substances on the left side of the arrow) are transformed into products (substances on the right side of the arrow). All chemical reactions must be balanced – the number of atoms of each element must be the same on each side of the equation.

Chemical Equations The coefficients in an equation give the molar ratios of the reactants and products. 2 H2(g) + O2(g) → 2 H2O(l) This tells us that 2 moles of hydrogen react with 1 mole of oxygen to produce 2 moles of water.

2 H2(g) + O2(g) → 2 H2O(l) The mole ratio is a ratio of the coefficients in the balanced chemical equation. When working stoichiometry problems, the coefficient for the unknown is always on top. The mole ratio of hydrogen to oxygen is 2 to 1. The mole ratio of oxygen to water is 1 to 2.

Homework Complete the “Types of Matter” worksheet Draw and label a curve showing the changes in the three common physical states of matter. Indicate the names of the changes (in both directions), as well whether the changes in energy are changes in kinetic energy or potential energy.