Friday, Sept. 20 th : “A” Day Monday, Sept. 23 rd : “B” Day Agenda  Ch 1 Tests  Start Ch. 2: Matter and Energy  Section 2.1: “Energy” Energy, physical/chemical changes, evaporation, exothermic/endothermic, law of conservation of energy  Homework: Pg. 45: #1-13 Phase Change Diagram WS Concept Review: “Energy” **Quiz over section 2.1 next time!**

Ch 1 Tests “The Science of Chemistry” ClassAverage Score (out of 60) Percentage 2A 4A 1B 3B

Ch 2: Matter and Energy Sec. 2.1: “Energy”  Energy: the capacity to do work, such as moving an object, forming a new compound, or generating light.  Energy is always involved when there is a change in matter.

Changes in Matter can be Physical or Chemical  Physical change: a change of matter from one form to another without a change in chemical properties.  The chemical nature of the substance does not change. Examples: Ice melting Water boiling

Changes in Matter can be Physical or Chemical  Chemical change: a change that occurs when one or more substances change into entirely new substances with different properties.  A chemical change occurs whenever a new substance is made. Example: Reaction of hydrogen + oxygen to produce water +

Every Change in Matter Involves a Change in Energy  All physical AND chemical changes involve a change in energy.  Sometimes, energy must be supplied for the change in matter to occur. Example: for ice to melt, energy must be supplied so that the particles have enough energy to slide past one another

Every Change in Matter Involves a Change in Energy  If more energy is added to the melted ice and the boiling point is reached, the particles of the liquid will leave the liquid’s surface through evaporation.  Evaporation: the change of a substance from a liquid to a gas.

Energy and Change  Sometimes, energy is released when a change in matter occurs. Examples: Energy is released when a vapor turns into a liquid (condensation) Energy is released when a liquid turns into a solid (freezing) Energy is released when hydrogen and oxygen combine to form water

Endothermic/Exothermic Processes  Endothermic: describes a process in which heat is absorbed from the environment Examples Ice melting Water boiling

Endothermic/Exothermic Processes  Exothermic: describes a process in which a system releases heat into the environment Examples Water freezing Water condensing into liquid from vapor Hydrogen + oxygen form water

Conservation of Energy  Law of conservation of energy: the law that states that energy cannot be created or destroyed but can be changed from one form to another.  During any chemical or physical change, the total quantity of energy remains constant.

Energy is Often Transferred  To keep track of energy changes, chemists use the terms system and surroundings.  System: all of the components that are being studied at any given time  Surroundings: everything outside of the system

Conservation of Energy in a Chemical Reaction  An exothermic process involves a transfer of energy from a system to its surroundings.  An endothermic process involves a transfer of energy from the surroundings to the system.  The total energy of the systems and their surroundings remains the same.

Conservation of Energy in a Chemical Reaction Does this chart represent an exothermic or endothermic process?

Energy Can be Transferred in Different Forms  The transfer of energy between a system and its surroundings can involve different forms of energy: Chemical Mechanical Light Heat Electrical Sound

Heat  Heat: the energy transferred between objects that are at different temperatures; energy is always transferred from higher-temperature objects to lower-temperature objects until thermal equilibrium is reached.  Kinetic energy: the energy of an object that is due to the object’s motion

Energy Can be Released or Absorbed as Heat  Exothermic reaction Energy is released as heat  Endothermic reaction Energy is absorbed as heat

Heat is Different From Temperature  Temperature: a measure of how hot or cold something is; specifically, a measurement of the average kinetic energy of the particles in an object.

Temperature is Expressed Using Different Scales  The two temperature scales that are used in chemistry are: Celsius, ˚C Kelvin, K  0˚C = freezing point of water  0 K = absolute zero, the temperature at which the minimum average kinetic energies of all particles occur

To find °C = T(K) To find K = t(˚C) + 273

Transfer of Heat May Not Affect Temperature Heating Curve for Water

Transfer of Heat May Not Affect Temperature  Notice that the temperature only increases when the substance is in the solid, liquid, or vapor states.  The temperature does not increase when the solid is changing to a liquid or when the liquid is changing to a gas.  The energy that is added is used to change state.

Specific Heat  Specific Heat: the quantity of energy, as heat, that must be transferred to raise the temperature of 1 g of a substance 1 K or 1˚C.  The SI unit for energy is the joule (J)  Specific heat is expressed in: joules per gram kelvin (J/g · K)

Specific Heat  Metals tend to have low specific heats, which indicates that relatively little energy must be transferred as heat to raise their temperatures.  Water has an extremely high specific heat.  This is why a metal pot gets hot fast but the water inside it takes a long time to warm up.

Specific Heat  This is also why Lake Michigan is always so cold, even in August!  It takes a long time to warm something, like water, that has a high specific heat.

Homework  Section 2.1 review, pg. 45: #1-13  Phase Change Diagram worksheet  Homework: Concept Review: “Energy” **Next time: Sec 2.1 Quiz**