Regents Chemistry

Regents Chemistry Topic IV Physical Behavior of Matter

Different Phases of Matter • An element, compound or mixture can exist in the form of a solid, liquid or a gas • Solid – rigid form, definite volume and shape, strong attractive forces and crystalline structure • Liquid – not held together as well, can move past one another, no definite shape but definite volume • Gas – minimal attractive forces, no definite shape or volume, expand to shape of container

Other Phases • Vapor – is the gaseous phase of a substance that is a liquid or a solid at normal conditions: ex: water vapor • Plasma – is a gas or vapor in which some or all of the electrons have been removed from the atoms. ex: In a planet’s core!

Heating and Cooling Curves • Heating Curves: Constant rate of heating of a substance over time – endothermic process!

What Can We Learn From a Heating Curve? • AB: heating of a solid, one phase present, kinetic energy increases • BC: melting of a solid (melting), two phases present, potential energy increases, kinetic energy remains constant • CD: heating of a liquid, one phase present, kinetic energy increases

What Can We Learn From a Heating Curve? • DE: boiling of a liquid (Vaporization), two phases present, potential energy increases, kinetic energy remains constant • EF: heating of a gas, one phase present, kinetic energy increases ***We can tell when the kinetic energy remains constant because the temperature is not increasing!***

Cooling Curves • Shows the constant rate of cooling of a gas at high temperature – an exothermic process

Summary of a Cooling Curve • AB:cooling of a gas (vapor), one phase present, kinetic energy decreases • BC: condensation of the gas (vapor) to liquid, two phases present, potential energy decreases, kinetic energy remains constant • CD: cooling of a liquid, one phase present, kinetic energy decreases

Summary of a Cooling Curve • DE: solidification (freezing) of a liquid, two phases present, potential energy decreases, kinetic energy remains the same • EF: cooling of a solid, one phase present, kinetic energy decreases

Substances That Do Not Follow the Curves • Some substances change directly from a solid to a gas – Sublimation • Example: CO2 changes from a solid to a gas a normal atmospheric pressure • Some substances change directly from gas to a solid – Deposition

Practice Problem Which portions of the graph represent times when heat is absorbed and potential energy increases while kinetic energy remains constant? worksheet

Regents Chemistry • Temperature Scales

Temperature Scales • Celsius ° C • Based on boiling point/freezing point of water • Kelvin K • Based on absolute zero • Fahrenheit° F • Used in U.S. and Great Britain

Conversions • Key Equations Celsius to Kelvin K = °C + 273 Fahrenheit to Celsius °C = 5/9 (°F - 32) Kelvin to Celsius °C = K - 273 Celsius to Fahrenheit °F = 9/5(°C) + 32 **Add the conversions on the right to your worksheet

Practice Problems • Convert 10 °C to °F °F = 9/5(°C) + 32 = 9/5 (10 °C) + 32 = 50°F • Convert 25°C to K • K = °C + 273

Worksheet • Add the Fahrenheit and Celsius conversions to worksheet • Finish worksheet using p. 36 - 43 from text • Answer problems on p. 52 #71-76 on worksheet - write out question and answer • Homework: p.52 #77,78,79 (a-e)

Regents Chemistry • Measurement of Heat Energy

Energy and Energy Changes • Energy is the capacity to do work. In other words, it allows us to do things! • Energy surrounds us and is involved in all of life’s daily functions. • It comes in many forms!

Energy and Energy Changes • Energy can be used to change the temperature of a substance • As we heat a substance (put in heat), the vibration of molecules in a substance increases. • Example: When a solid is heated, the molecules vibrate until they break free and the substance melts.

Specific Heat Capacity • The specific heat capacity of a substance is the amount of heat required to raise 1 gram of the substance by 1 degree Celsius • For water it is 4.184 J / g• K • Compared to other substances, water has a very high specific heat..what does this mean?

Specific Heat Capacities • Check out the specific heat capacities of different substances!

Measurement of Heat Energy • Question: You pool absorbs how many much heat energy when it warms from 20 °C to 30 °C? • It easy is we use a formula on our reference tables! q = mCT

This means what?.. q = mCT • q = amount of heat absorbed or lost • m = mass in grams • C = specific heat • T = difference in temperature

Back to our problem… • Question: You mini - pool containing 100,000 g of water absorbs how many much heat energy when it warms from 20 °C to 30 °C? • q = mCT q = (100,000 g)(4.184 J / g• K) (10 °C) = q = 4,184,000 Joules!

Rearranging the formula.. • You need to be able to solve for any of the variables in the equation q = mCT

Making it easy.. • If we are finding the heat change during the melting or boiling phases, we can use the Heat of Fusion or the Heat of Vaporization.. • Why?? Because temperature remains constant during these periods!

Heat of Fusion and Vaporization • Heat of Fusion – amount of heat energy required to melt a unit mass of a substance • For water : HOF = 334 J/g • Heat of Vaporization – amount of energy required to convert a unit mass from liquid to vapor phase • For Water: HOV = 2260 J/g

Practice Problem • How many joules are required to melt 255 g of ice at 0°C? • q = m x Heat of Fusion q = 255 g x 334 J/g = 85, 170 J

Measuring Heat Change • Calorie = the amount of energy(heat) required to raise the temperature of one gram of water by one Celsius degree. • 1 Calorie (cal) = 4.184 Joules (J) Metric system SI system

Converting Calories to Joules • Convert 60.1 cal of energy into joules 60.1 cal X 4.184 J = 251 J 1 cal = 4.184 J 1 cal

Converting Joules to Calories • Convert 50.3 J to cal 1 cal = 4.184 J 50.3 J X 1 cal = 12.0 cal 4.184 J

Kilojoules and Kilocalories • The prefix kilo means 1000 • energy is often expressed in kilos because the numbers are large • We can use Dimensional Analysis to convert. 4.0 J x 1 kJ = 0.0040 kJ 1000 J

Converting kilojoules to kilocalories 1 cal = 4.184 J 1000 kcal = 4184 kJ 500.0 kJ x 1000 kcal = 2092 kcal 4184 kJ

Regents Chemistry • Behavior of Gases

Behavior of Gases • Scientists construct models to explain the behavior of substances • Gas laws are used to describe the behavior of gases • We will focus on the kinetic molecular theory, which describes the relationships among pressure, volume, temperature, velocity, frequency and force of collisions

Kinetic Molecular Theory • Major Ideas: 1. Gases contain particles (usually molecules or atoms) that are in constant, random, straight-line motion 2. Gas particles collide with each other and with the walls of the container. These collisions may result in a transfer of energy among the particles, but there is no net loss of energy as the result of the collisions. Said to be “Perfectly Elastic”.

Kinetic Molecular Theory 3. Gas particles are separated by relatively great distances. because of this, the volume occupied by the particles themselves Is negligible and need not be accounted for. 4. Gas particles do not attract each other.

Relationship Between Pressure and # of gas Particles • Kinetic Molecular Theory explains why gases exerts pressure • Gas particles collide with each other and the walls of the container • Thus pressure is exerted on the walls • The greater the number of air particles, the greater the pressure • Pressure and number of gas molecules are directly proportional

Relationship Between Pressure and Volume of a Gas • If you compress the volume of a container, the particles hit the walls more often and pressure increases. The reverse is also true!

Relationship Between Temperature and Pressure of a Gas • Temperature of a substance is defined as the measure of the average kinetic energy of the particles • Kinetic Energy is given by the formula KE = ½ mv2 • So, as the temperature rise, the average kinetic energy of the particles increase • Increase is not due to mass, but an increase in velocity of the particles, causing them to hit the walls of the container with greater force (pressure)

Relationship Between Temperature and Pressure of a Gas At constant volume, as the temperature of the gas Increases, the pressure it exerts increases

Relationship of Temperature and Volume of a Gas At constant pressure, As the temp of the gas Increases, the volume It occupies increases

Relationship Between Temperature and Velocity • As temperature increases, the kinetic energy of the particles increase • What causes the increase in temp? • The increase in velocity of the particles • The higher the average velocity of the particles, the greater the temperature KE = ½ mv2

Combined Gas Law Equation P and V must be in the same units and T must be in Kelvin! P1V1 P2V2 T1 T2 This law can be used to solve problems involving the gas properties of temperature(T), volume(V) and pressure(P), whenever two or more of these properties are involved

Common Units of Variables • Standard temperature and pressure (STP) is defined as • One atmosphere of pressure and a temperature • of 0 C (273K) • Pressure is defined as force per unit area. • In chemistry, pressure is expressed in units of: • torr, millimeters of mercury (mm Hg), atmospheres (atm) • and kilopascals (kPa). • Normal atmospheric pressure is: • 760 torr, 760 mm Hg, 1 atm and 101.3 kPa

Ideal vs. Real Gases The KMT describes Ideal gases, but real gases behave differently in two ways • 1. Real gas particles DO ATTRACT at low temperatures • Ex: ozone! • 2. The volume real gas particles occupy at high pressures becomes important.. • Real behaves most like ideal at high temperatures and low pressures

Gas Law Sample Problem worksheet

Regents Chemistry • Agenda 2/26/04 Thursday • Review Gases worksheet • Discuss Quiz for tomorrow • HW: STUDY!

Regents Chemistry