Ch. 1(1) Fundamental definitions in Chemistry - states of matter, properties of matter, energy.pdf

Chemistry The Molecular Nature of Matter and Change Ninth Edition Martin S. Silberberg and Patricia G. Amateis ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGr...

Chemistry The Molecular Nature of Matter and Change Ninth Edition Martin S. Silberberg and Patricia G. Amateis ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education. Chapter 1 – Keys to Studying Chemistry: Definitions, Units, Problem Solving (CHEM 101 Review) 1.1 Some Fundamental Definitions 1.3 Measurement, Units, and Chemical Problem Solving 1.4 Uncertainty in Measurement: Significant Figures ©McGraw-Hill Education. 1.1 Chemistry: some definitions Chemistry is a science. (Alchemy was religious philosophy.) Chemistry is the science of composition, structure, properties, and reactions of matter, and the interaction of matter with energy. Matter in modern chemistry - from individual atoms and molecules, elements, compounds to: – crystals, glasses, amorphs, liquid crystals, liquids, gases – aggregates of molecules (supramolecules, colloids, polymers) – thick or thin films, alloys, composite solids (materials science) – minerals, rocks, meteorites (geochemistry, cosmochemistry) – Biochemistry and chemical biology ©McGraw-Hill Education. Definitions Matter: anything that has both mass and volume – the “stuff” of the universe: books, planets, trees, professors, students. Composition: the types and amounts of simpler substances that make up matter. Examples: – Elemental composition of a pure chemical compound – Molecular composition of impure material (a mixture of pure compounds) Properties: the physical and chemical characteristics that give each substance a unique identity. Examples: – Physical properties: state (solid, liquid, gas), density, color, transparency to light, melting temperature, boiling temperature, etc. – Chemical properties: stability in air, reactivity in acids or bases, reactivity with air at higher temperatures, etc. ©McGraw-Hill Education. The States of Matter The three common states: A solid has a fixed shape and volume. Solids may be hard or soft, rigid or flexible. A liquid has a varying shape that conforms to the shape of the container, but a fixed volume. A gas has no fixed shape or volume. Other states of the matter: Liquid crystals Amorphous (non-crystalline) solids Plasma = ionized gas, typically emitting light (e.g., fire, neon light, stars) ©McGraw-Hill Education. Physical States of Matter at Molecular Level In a solid, particles do not translate with respect to each other and are closely packed together. In a liquid, the particles continuously move with respect to each other but maintain close packing to form aggregates. Aggregates are also close-packed. ©McGraw-Hill Education. In a gas, particles are no longer packed. ©McGraw-Hill Education. Physical and Chemical Properties Physical Properties – properties a substance shows by itself without interacting with another substance – Examples: color, melting point, boiling point, density, refractive index Chemical Properties – properties a substance shows as it interacts with, or transforms into, other substances – Examples: flammability, corrosiveness, temperature stability, stability in air, stability in solvents, compression stability (explosiveness), stability in time, stability in visible or ultraviolet light, stability in the presence of other chemicals (acids, bases, etc.) ©McGraw-Hill Education. The Distinction Between Physical and Chemical Change Fig 1.2 ©McGraw-Hill Education. (A) © Paul Morrell/Stone/Getty Images; (B) © McGraw-Hill Education/Stephen Frisch, photographer Visualizing Change on the Atomic Scale Sample Problem 1.1 – Problem and Plan PROBLEM: The scenes below represent an atomic-scale view of substance A undergoing two different changes. Decide whether each scene shows a physical or a chemical change. PLAN: We need to determine what change is taking place. The numbers and colors of the little spheres that represent each particle tell its “composition”. If the composition does not change, the change is physical, whereas a chemical change results in a change of composition. ©McGraw-Hill Education. Sample Problem 1.1 – Solution SOLUTION: Each particle of substance A is composed of one blue and two red spheres. Sample B is composed of two different types of particles – some have two red spheres while some have one red and one blue. As A changes to B, the chemical composition has changed. A → B is a chemical change. ©McGraw-Hill Education. Sample Problem 1.1 – Solution, Cont’d SOLUTION: Each particle of C is still composed of one blue and two red spheres, but the particles are closer together and are more organized. The composition remains unchanged, but the physical form is different. A → C is a physical change. ©McGraw-Hill Education. What is Copper? A Metal with Characteristic Properties In Chemistry we study the observable (detectable) changes in matter and energy to understand their unobservable causes. ©McGraw-Hill Education. (copper) © McGraw-Hill Education/Mark Dierker, photographer; (candlestick) © Ruth Melnick; (copper carbonate, copper reacting with acid, copper and ammonia) © McGraw-Hill Education/Stephen Frisch, photographer Temperature and Change of State Temperature is a physical property (quantity) that expresses numerically on a quantitative scale what humans perceive as hotness or coolness. Quantitative scales: absolute temperature of matter (Kelvin), relative scale with respect to water melting (0°Celsius) and boiling (100°C) at normal air pressure. A change of state is a physical change. – Physical form changes, composition does not. Changes in physical state are reversible – by changing the temperature or pressure. A chemical change cannot simply be reversed by a change in temperature (in general). ©McGraw-Hill Education. Distinguishing Between Physical and Chemical Change Sample Problem 1.2 – Problem and Plan PROBLEM: Decide whether each of the following processes is primarily a physical or a chemical change, and explain briefly: (a) Frost forms as the temperature drops on a humid winter night. (b) A cornstalk grows from a seed that is watered and fertilized. (c) A match ignites to form ash and a mixture of gases. (d) Perspiration evaporates when you relax after jogging. (e) A silver fork tarnishes slowly in air. PLAN: “Does the substance change composition or just change form?” ©McGraw-Hill Education. Sample Problem 1.2 – Solution (a) Frost forms as the temperature drops on a humid winter night – physical change (b) A cornstalk grows from a seed that is watered and fertilized – chemical change (c) A match ignites to form ash and a mixture of gases – chemical change (d) Perspiration evaporates when you relax after jogging – physical change (e) A silver fork tarnishes slowly in air – chemical change ©McGraw-Hill Education. Energy (Physics refresher) Energy is the real or potential ability of an object to move relative to other objects. Kinetic Energy is mechanical energy of an object in motion. 1 2 – 𝐾𝐸 = 𝑚𝑢2 (m is the mass and u is the linear speed of the object) – Since mass does not change upon moving, an object moving at constant linear speed u has a constant Kinetic Energy. – An accelerating object gains Kinetic Energy. – A decelerating (slowing down) object loses Kinetic Energy. Potential Energy is energy due to the position of an object in a force field (gravity, electric, magnetic, etc.). An object with potential energy is either at rest (cannot move because of a barrier) or is accelerating / decelerating. An object moving at constant linear speed and Kinetic Energy does not have potential energy. An accelerating or decelerating object has both potential and kinetic energies. ©McGraw-Hill Education. Spontaneous Energy Changes in Nature Lower energy states within the force field are more stable (have lower potential energy) and are favored over higher energy states (with higher potential energy). An object with potential energy (i.e., in a force field) moves spontaneously in a direction toward the lowest potential energy within the force field if no barrier is present. Energy is neither created nor destroyed – it is conserved – must be converted from one form to another (potential to kinetic energy or vice versa) – More on this topic in subchapter 6.1. ©McGraw-Hill Education.