Updated August 2006 Created by C. Ippolito August 2006 Energy Objectives: 1.identify various forms of energy 2.describe energy changes during a chemical reaction 3.distinguish between heat energy and temperature 4.solve calorimetry problems 5.describe interactions between electrostatic charges

Created by C. Ippolito August 2006 Updated August 2006 Concept of Energy EnergyEnergy –ability to do work –can be changed into work under proper conditions –can be converted from one form into another –can be transmitted from one particle to another WorkWork –done when an object, in response to a force (push or pull), moves some distance –work = force x distance

Created by C. Ippolito August 2006 Updated August 2006 Mechanical Energy energy possessed by macroscopic (large) particles –Potential Energy –Potential Energy (E P ) depends on the position of the object in respect to other objects stored energy –Kinetic Energy –Kinetic Energy (E K ) depends upon the motion of an object in respect to other objects “working” energy

Created by C. Ippolito August 2006 Updated August 2006 Nonmechanical Energy energy associated with submicroscopic (small) particles –chemical energy –electrical energy –electromagnetic energy a.k.a. radiant energy –sound energy –magnetic energy –heat energy joule (J) is the SI unit that measures energy –named to honor James Joule, British scientist to study all forms of energyJames Joule

Created by C. Ippolito August 2006 Updated August 2006 Matter and Energy Law of the Conservation of MatterLaw of the Conservation of Matter –Matter is always conserved. This means the amount of matter is constant, it is neither created nor destroyed. It can only change form. Law of the Conservation of EnergyLaw of the Conservation of Energy –Energy is always conserved. The amount of energy in the universe is also constant, it is neither created nor destroyed. It too can only change form. Albert Einstein –Matter can be changed into energy and energy can be changed into matter with his now famous equation E = mc 2 –Law of the Conservation of Mass- Energy Mass-Energy is always conserved. The amount of Mass-Energy in the universe is also constant, it is neither created nor destroyed. It too can only change form.

Created by C. Ippolito August 2006 Updated August 2006 Energy and Chemical Change All chemical changes are accompanied by a change in energy –Endothermic Reaction Heat energy is absorbed Products have more energy than reactants Surroundings become colder –Exothermic Reaction Heat energy is released Products have less energy than reactants Surroundings become warmer Activation EnergyActivation Energy –Minimum amount of energy needed to start any chemical reaction

Created by C. Ippolito August 2006 Updated August 2006 Heat Energy and Temperature Temperature based on “hotness” and “coldness” –Celsius Scale Anders Celsius 0 o C water freezes100 o C water boils –Kelvin scale William Kelvin Based on theoretically lowest temperature of absolute zero where all molecular motion stops

Created by C. Ippolito August 2006 Updated August 2006 Temperature Conversions To convert Celsius to Kelvin –Add 273 to Celsius temperature 50 o C = ? K 50 o C = 323 K To convert Kelvin to Celsius –Subtract 273 from Kelvin temperature 30 K = ? o C 30 K – 273 = -243 o C

Created by C. Ippolito August 2006 Updated August 2006 Heat Measurement Calorimeter –Apparatus used to measure heat by rise or fall of temperature of water Specific Heat Capacity (C P ) –amount of joules needed to raise 1g of a substance 1 o C –measured as –listed in “Handbook of Chemistry and Physics”“Handbook of Chemistry and Physics” C P water = 4.18 J/g  o C C P aluminum = J/g  o C

Created by C. Ippolito August 2006 Updated August 2006 Heat Calculations Equation: –Heat transferred = m   T  C P water M = mass of water  T = change in water temperature C Pwater = 4.18 J/g  o C How much energy is needed to raise 40 g of water from 20.0 o C to 36 o C? Known: C Pwater = 4.18 J/g  o C T initial = 20 o C T final = 36 o C m = 40 g Unknown: Heat transferred

Created by C. Ippolito August 2006 Updated August 2006 Heat Calculations (con’t) How much heat energy is lost when a solid ingot of aluminum with a mass of g cools from 660 o C to 25.0 o C? Known: C Paluminum = J/g  o C T initial = 660 o C T final = 25.0 o C m = g Unknown: Heat transferred