Chapter 2 Matter and Energy

Chemistry is the study of matter, its transformations, and the energy changes that accompany those transformations.

Chapter 2Matter and Energy

2.1 Matter, Mass and Weight Matter Anything that has mass and takes up space is called matter. Mass Mass of an object is determined by its resistance in motion and is a measure of the quantity of matter. Weight Weight is the force of gravity. The weight of an object is proportional to the mass: Weight = mass x acceleration of gravity

2.2 States of Matter States of Matter: Gas, Liquid, Solid The air you breathe is a gas. The water you drink is a liquid. The food you eat is a solid.

2.2 States of Matter: Gas • Gas is a fluid form of matter. It fills any container it occupies. • At low pressure ( p < 1 atm) particles are far apart compared with their dimension. Particles are independent of one another. Attraction among particles is important only at high pressure (p > 30 atm). • Particles are moving in random fashion. At room temperature the speed of carbon dioxide molecule is around 400 m/s. The speed at which particles move is faster at higher temperatures and slower at lower temperatures.

2.2 States of Matter: Solid • Solid is a rigid form of matter. Shape and volume are constant. • Particles are close together. Particle interaction is very strong. • Particles rotate and vibrate in fixed positions relative to one another.

2.2 States of Matter: Liquid • Liquid is a fluid form of matter. • Liquid has a constant volume but takes the shape of the part of the container it occupies. • Particles move freely among themselves, but clump together.

2.2 States of Matter

2.3 Properties and Changes • A physical property of a substance is a characteristic that we observe or measure without changing the identity of the substance. • A chemical property of a substance is a characteristic that we observe or measure only by changing the identity of the substance.

2.3 Properties and Changes Physical Changes • Changes in physical form of matter without changes in chemical identity. No new substance formed Examples: • Fusion, solidification • Vaporization, condensation • Sublimation, deposition

2.3 Properties and Changes In a Physical Change, the Molecules are Unchanged:

2.3 Properties and Changes Chemical Changes Chemical identity of a substance is destroyed A new substance is formed Examples: Water decomposes to hydrogen and oxygen gases when subjected to an electrical current Iron rusts Food is digested

Properties and Changes In a Chemical Change, the Molecules Change:

2.3 Properties and Changes Chemical Properties The types of chemical change a substance is able to participate in. Examples: A chemical property of water is that it can be decomposed to its elements when subjected to an electrical current. A chemical property of iron is that it will rust under certain conditions.

2.3 Properties and Changes

2.4 Substances and Mixtures Pure Substance A sample consisting of only one kind of matter, either compound or element; made up entirely of one kind of particle. Unique set of physical and chemical properties. Cannot be separated into parts by a physical change.

2.4 Substances and Mixtures Mixture A sample of matter that consists of two or more substances. Physical and chemical properties of a mixture vary with different relative amounts of the parts. Can be separated into parts via physical processes.

Pure water has a constant boiling point—a physical property. The boiling point of a mixture (solution) changes as the composition of the mixture changes. 2.4 Substances and Mixtures

2.4 Substances and Mixtures You cannot distinguish a pure substance from a mixture of uniform appearance by observation alone at the macroscopic level.

2.4 Substances and Mixtures Homogeneous A sample that has uniform appearance and composition throughout. Solution A homogeneous mixture of two or more components. Heterogeneous A sample with different phases, usually visible.

Substances and Mixtures Homogeneous Matter may be Either a Pure Substance or a Mixture:

2.5 Separation of Mixtures Most natural substances are mixtures. Separation processes are an important part of chemistry. Nitrogen and oxygen are separated from the mixture called air. Pure water is separated from the mixture called natural water.

2.5 Separation of Mixtures A Physical Property, Magnetism, Allows a Mixture of Iron and Sulfur to be Separated:

2.5 Separation of Mixtures Distillation Separation of the parts of a mixture by heating a liquid solution until one component boils, changing into the gaseous state. The pure substance in the gaseous state is then collected and cooled into the liquid state. Boiling is a physical change. Distillation allows components in a homogeneous mixture to be separated into one or more pure substances.

2.5 Separation of Mixtures Laboratory Distillation Apparatus:

2.5 Separation of Mixtures Filtration Separation of the components of a mixture by physical means by using a porous medium, such as filter paper, to separate components based upon relative particles sizes. Filtration is based on the physical properties of a mixture: The particle sizes of a component to be separated must be significantly larger or smaller than the pore size of the filtration medium.

2.5 Separation of Mixtures Gravity Filtration

2.6 Elements and Compounds Element Pure substance that cannot be decomposed into other pure substances by ordinary chemical means. Atom Smallest particle of an element that can combine with atoms of other elements to form compounds. Compound Pure substance that can be broken down into two or more other pure substances by a chemical change.

2.6 Elements and Compounds Mixtures are separated into pure substances by physical means; compounds are separated into pure substances by chemical changes.

2.6 Elements and Compounds Elements At least 88 elements occur in nature. Examples: copper, sulfur, gold, silver 11 elements occur in nature at room temperature as gases; 2 occur as liquids (mercury and bromine); the others occur as solids.

2.6 Elements and Compounds Major Elements of the Human Body ElementPercentage Composition by Number of Atoms Hydrogen 63.0 Oxygen 25.5 Carbon 9.45 Nitrogen 1.35 These four elements make up 99.3% of the atoms in your body.

2.6 Elements and Compounds Elemental Symbols The first letter of the name of the element, written in uppercase, is often its symbol. Examples: Hydrogen, H; Oxygen, O; Carbon, C If more than one element begins with the same letter, a second lowercase letter is added. Examples: Helium, He; Chlorine, Cl

2.6 Elements and Compounds Chemical Formulas Symbolic representations of the particles of a pure substance. A combination of the symbols of all the elements in a substance. The formula of most elements is the same as the symbol of the element, e.g., helium, He; sodium, Na. Other elements exists in nature as molecules and their formulas indicate the number of atoms of the element in the molecule, e.g., hydrogen, H2; oxygen, O2.

2.6 Elements and Compounds Formula Unit Molecule or simplest ratio of particles for non-molecular species. Ammonia molecules have the formula NH3: 1 atom of nitrogen and 3 atoms of hydrogen. Magnesium chloride has the formula unit MgCl2.

2.6 Elements and Compounds Law of Constant Composition Any compound is always made up of elements in the same proportion by mass (weight). No matter its source, water (H2O) is 11.1 parts hydrogen per 88.9 parts oxygen.

2.6 Elements and Compounds The Properties of a Compound are Different from the Properties of the Elements that Make Up the Compound: Water, H2O Liquid at 25°C, melts at 0°C, boils at 100°C Hydrogen, H2 Gas at 25°C, melts at –259°C, boils at –253°C Oxygen, O2 Gas at 25°C, melts at –219°C, boils at –183°C

2.6 Elements and Compounds Summary of the Classification System for Matter:

2.7 Electrical Character of Matter Matter has electrical properties. There are only two types of electrical charge, positive and negative. • Two objects having the same charge, both positive or both negative, repel each other. • Two objects having different charges, one positive and one negative, attract each other.

2.7 Electrical Character of Matter

2.7 Electrical Character of Matter Electrostatic Attraction and Repulsion

2.8 Chemical Change Chemical Equation A symbolic representation of chemical change, with the formulas of the beginning substances to the left of an arrow that points to the formulas of the substances formed. Reactant Original substance Product Substance formed as a result of chemical change 2 H2O 2 H2 + O2 Reactant Products

2.8 Chemical Change Exothermic Reaction A chemical change that releases energy to its surroundings. Example:Burning charcoal C + O2 CO2 + energy

2.8 Chemical Change Endothermic Reaction A chemical change that absorbs energy from its surroundings. Example: Decomposition of water to its elements 2 H2O + energy 2 H2 + O2

2.9 Conservation Laws • Law of Conservation of Mass: In any ordinary chemical change, total mass of reactants = total mass of products number of atoms of each element is the same before and after the reaction.

2.9 Conservation Laws • Law of Conservation of Charge: In any ordinary chemical change, total charge of reactants = total charge of products Electric charge is unchanged in the reaction • NaCl ---------> Na+ + Cl-

2.9 Conservation Laws • Law of Conservation of Energy • Energy is the capacity to do work or supply heat. A system can exchange its energy with its surrounding in two forms: heat and work. • Heat is the transfer of energy as a result of a difference in temperature. Work is done when an object is moved against an opposing force. Heat and work are equivalent ways of changing the energy of a system. Energy of an isolated system is conserved; it is neither created nor destroyed.

2.9 Conservation Laws • Law of Conservation of Energy The form (as heat or as work) in which energy is released depends on how the reaction takes place. For example in normal condition the reaction between hydrogen and oxygen releases heat 2 H2 + O2 ---------> 2 H2O + energy as heat But this same reaction in a fuel cell can generate electricity and produce work 2 H2 + O2 ---------> 2 H2O + energy as work

Homework • Law of Conservation of Energy • You need to have a notebook for homework. • Homework notebook will be checked on days of the exam. • Homework for chapter 2: 23, 29, 39, 43, 51, 53, 55, 66, 71, 72, 73

Chapter 2 Matter and Energy