Solid, Liquid, Gas (a) Particles in solid (b) Particles in liquid (c) Particles in gas

Solid H2O(s) Ice Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31

Ice H2O(s) Ice Photograph of ice model Photograph of snowflakes Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Liquid In a liquid H2O(l) Water molecules are in constant motion there are appreciable intermolecular forces molecules are close together Liquids are almost incompressible Liquids do not fill the container some writing from Kotz (PowerPoint online) H2O(l) Water Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31

Gas H2O(g) Steam Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31

Liquids The two key properties we need to describe are EVAPORATION and its opposite CONDENSATION add energy and break intermolecular bonds EVAPORATION CONDENSATION release energy and form intermolecular bonds

States of Matter Solid, Liquid, Gas are the three states of matter we will deal with. Plasma and Neutron star are also states of matter. For more information about plasma and neutron stars try the following links: Coalition for Plasma Science – What is plasma? http://www.plasmacoalition.org/what.htm Neutron Stars and Pulsars – Introduction http://imagine.gsfc.nasa.gov/cgi-bin/print.pl

Gas, Liquid, and Solid Gas Liquid Solid Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 441

States of Matter Solid Liquid Gas Holds Shape Fixed Volume In a solid the molecules are closely bound to one another by molecular forces. A solid holds its shape and the volume of a solid is fixed by the shape of the solid. Liquid In a liquid the molecular forces are weaker than in a solid. A liquid will take the shape of its container with a free surface in a gravitational field. In microgravity, a liquid forms a ball inside a free surface. Regardless of gravity, a liquid has a fixed volume. Gas In a gas the molecular forces are very weak. A gas fills its container, taking both the shape and the volume of the container Solid Liquid Gas heat heat Holds Shape Fixed Volume Shape of Container Free Surface Fixed Volume Shape of Container Volume of Container

Some Properties of Solids, Liquids, and Gases Property Solid Liquid Gas Shape Has definite shape Takes the shape of Takes the shape the container of its container Volume Has a definite volume Has a definite volume Fills the volume of the container Arrangement of Fixed, very close Random, close Random, far apart Particles Interactions between Very strong Strong Essentially none particles The three common phases (or states) of matter are gas, liquid, and solid 1. Gases a. Have the lowest density of the three states of matter b. Are highly compressible c. Completely fill any container in which they are placed d. Their intermolecular forces are weak e. Molecules are constantly moving independently of the other molecules present 2. Solids a. Dense b. Rigid c. Incompressible d. Intermolecular forces are strong e. Molecules locked in place 3. Liquids b. Incompressible c. Flow readily to adapt to the shape of the container d. Sum of the intermolecular forces are between those of gases and solids • The state of a given substance depends strongly on conditions

Evaporation To evaporate, molecules must have sufficient energy to break IM forces. Molecules at the surface break away and become gas. Only those with enough KE escape. Breaking IM forces requires energy. The process of evaporation is endothermic. Evaporation is a cooling process. It requires heat.

Condensation Change from gas to liquid Achieves a dynamic equilibrium with vaporization in a closed system. What is a closed system? A closed system means matter can’t go in or out. (put a cork in it) What the heck is a “dynamic equilibrium?” What is condensation? Condensation is the formation of liquid drops from water vapor. It is the process which creates clouds, and so is necessary for rain and snow formation as well. Condensation usually occurs when a parcel of rising air expands and cools. If it cools enough, some of the water vapor molecules clump together faster than they are torn apart from their thermal energy. A very important part of this process is the release of the latent heat of condensation. This is the heat that was absorbed when the water was originally evaporated from the surface of the Earth. The heat removed from the surface through evaporation is released again up in the atmosphere when clouds form. This process keeps the Earth's climate cooler that it would otherwise be if there were no water. Another way in which condensation occurs is during the formation of dew.

Dynamic Equilibrium When first sealed, the molecules gradually escape the surface of the liquid. As the molecules build up above the liquid - some condense back to a liquid. The rate at which the molecules evaporate and condense are equal.

Rate of Vaporization = Rate of Condensation Dynamic Equilibrium As time goes by the rate of vaporization remains constant but the rate of condensation increases because there are more molecules to condense. Equilibrium is reached when: Rate of Vaporization = Rate of Condensation Molecules are constantly changing phase “dynamic” The total amount of liquid and vapor remains constant “equilibrium”

Vaporization Vaporization is an endothermic process - it requires heat. Energy is required to overcome intermolecular forces Responsible for cool earth Why we sweat

Energy Changes Accompanying Phase Changes Gas Vaporization Condensation Sublimation Deposition Energy of system Liquid Melting Freezing Solid Brown, LeMay, Bursten, Chemistry 2000, page 405

Thermochemistry The study of the changes in heat energy that accompany chemical reactions and physical changes

Thermochemistry Heat Temperature a form of energy. can be transferred between samples heat flows from matter at a higher temperature to matter at a lower temperature Temperature a measure of the average kinetic energy of the particles in a sample.

Thermochemistry Units of Heat Joule (SI unit) calorie Calorie cal the amount of energy required to raise the temperature of one gram of water one degree Celsius. Calorie Cal a dietary calorie. kilocalorie, kcal (1,000 calories)

Thermochemistry Enthalpy the heat content of a system represented by H only changes in enthalpy can be measured ∴ ΔH is used

Thermochemistry Specific heat capacity, cp the amount of energy required to raise the temperature of one gram of a substance one degree Celsius used in equation q = m x cp x ΔT

Thermochemistry q = m x cp x ΔT note that in the Metric System, Joules are the unit of measure for heat. Energy, or heat (J) Δ temp (°C) mass (g) specific heat (J/g•°C)

Heat capacity, cp

q = m x cp x ΔT A 45.0-gram sample of iron is heated from 25.0°C to 50.0°C. How much energy is required? (cp iron = 0.449 J/g°C) q = ? m = 45.0 g cp = 0.449 J/g°C ΔT = 50.0°C – 25.0°C = 25.0°C q = m cp ΔT q = 45.0g (0.449 J/g°C) (25.0°C) = 505.125 q = 505 J

2. What is the specific heat capacity of an object if a 12 2. What is the specific heat capacity of an object if a 12.5-gram sample is heated from 12.0°C to 28.0°C using 100.0 joules? q = 100.0 J m = 12.5 g cp = ? ΔT = 28.0 – 12.0 = 16.0°C q = m cp ΔT