Chapter 2 Section 1 ENERGY

Energy The ability to do work or cause change. (the first part is more a physics idea and the second a chemistry)The ability to do work or cause change. (the first part is more a physics idea and the second a chemistry) –Example: Energy is released in the explosive reaction that occurs between hydrogen and oxygen to form water

Physical Changes Review from CH. 1:Review from CH. 1: A change of matter from one form to another without a change in chemical properties.A change of matter from one form to another without a change in chemical properties. Examples: Ice melting and water boilingExamples: Ice melting and water boiling –It’s still water (meaning the identity has not changed 2 hydrogen atoms are bonded to 1 oxygen atom)! Only the physical state has changed!

Chemical Change A change that occurs when one or more substances change into an entirely new substance with different properties.A change that occurs when one or more substances change into an entirely new substance with different properties. When a new substance is formed you have a chemical change which is also a chemical reaction.When a new substance is formed you have a chemical change which is also a chemical reaction.

Every Change in Matter involves a Change in Energy All physical and chemical changes involve a change in energyAll physical and chemical changes involve a change in energy Evaporation – the change of a substance from a liquid to a gas. This change requires an INPUT of energy.Evaporation – the change of a substance from a liquid to a gas. This change requires an INPUT of energy. Condensation – when a vapor turns into a liquid. The change requires a release of energy.Condensation – when a vapor turns into a liquid. The change requires a release of energy. –When hydrogen and oxygen react to form water (chemical change) there is an explosion that signifies that energy is being released.

Reaction Types based on energy We can classify reactions as endothermic or exothermic depending upon whether it absorbs or releases energy.We can classify reactions as endothermic or exothermic depending upon whether it absorbs or releases energy.

Endothermic Process Any change in matter in which energy is absorbed.Any change in matter in which energy is absorbed. Examples: Melting of ice, boiling of water (physical changes)Examples: Melting of ice, boiling of water (physical changes) Examples: barium hydroxide + ammonium nitrate (chemical change)Examples: barium hydroxide + ammonium nitrate (chemical change) 3Fchttps:// 3Fchttps:// 3Fchttps:// 3Fc Both require an input of energy

Exothermic reaction Any change in matter in which energy is RELEASED.Any change in matter in which energy is RELEASED. Examples: Freezing water, condensation of water vapor (physical changes)Examples: Freezing water, condensation of water vapor (physical changes) Example: Hydrogen + Oxygen (chemical change)Example: Hydrogen + Oxygen (chemical change) Po Po

Law of Conservation of Energy During any physical or chemical change, the total quantity of energy remains constants.During any physical or chemical change, the total quantity of energy remains constants. Energy cannot be created or destroyed but can be changed from one form to anotherEnergy cannot be created or destroyed but can be changed from one form to another Pg.41 Figure 4Pg.41 Figure 4

Energy is often transferred SYSTEM – All the components that are being studied at any given time.SYSTEM – All the components that are being studied at any given time. SURROUNDINGS – Everything outside the system.SURROUNDINGS – Everything outside the system. Energy is often transferred back and forth between a system and its surroundingsEnergy is often transferred back and forth between a system and its surroundings Exothermic process – Transfer of energy from the system to the surroundingsExothermic process – Transfer of energy from the system to the surroundings Endothermic process – Transfer of energy from the surroundings to the systemEndothermic process – Transfer of energy from the surroundings to the system

Energy can be transferred in Different forms Energy, light, mechanical, heat, electrical, sound are different forms of energy.Energy, light, mechanical, heat, electrical, sound are different forms of energy. Thus, energy can be transferred in different forms.Thus, energy can be transferred in different forms. Photosynthesis – light energy is transferred from the sun to green plants.Photosynthesis – light energy is transferred from the sun to green plants.

HEAT The energy transferred between objects that are at different temperatures.The energy transferred between objects that are at different temperatures. Do you remember the direction heat always flows?Do you remember the direction heat always flows? –Warmer object to a cooler object THE MOST COMMON TRANSFERS OF ENERGY IN CHEMISTRY ARE THOSE THAT INVOLVE HEAT.

Energy can be released or absorbed as heat If energy is released during a reaction - exothermicIf energy is released during a reaction - exothermic –Ammonium Nitrate being ignited afe=active afe=active If energy is absorbed during a reaction – the reaction is classified as endothermicIf energy is absorbed during a reaction – the reaction is classified as endothermic –Baking bread

Heat is different from Temperature A measurement of the average kinetic energy of the random motion of particles in a substance.A measurement of the average kinetic energy of the random motion of particles in a substance. Think of heat as the energy that is transferred from a stove to water due to a temperature difference.Think of heat as the energy that is transferred from a stove to water due to a temperature difference.

Temperature is Expressed Using Different Scales Fahrenheit scale is not used in chemistryFahrenheit scale is not used in chemistry The SI unit for Temperature is the Kelvin,KThe SI unit for Temperature is the Kelvin,K Zero on the Celsius scale is the freezing point for waterZero on the Celsius scale is the freezing point for water Zero on the Kelvin scale is absolute zero, the temperature at which the minimum average kinetic energies of all particles occur.Zero on the Kelvin scale is absolute zero, the temperature at which the minimum average kinetic energies of all particles occur.

Converting between the Celsius and Kelvin scale t( o F) = (t ( o C) x 1.8) + 32 converting celsius to fahrenheitt( o F) = (t ( o C) x 1.8) + 32 converting celsius to fahrenheit t( o C) = (t( o F) – 32) / 1.8 converting fahrenheit to celsiust( o C) = (t( o F) – 32) / 1.8 converting fahrenheit to celsius t( o C) = t (K) K converting Kelvin to celsius t( o C) = t (K) K converting Kelvin to celsius t(K) = t ( o C) o C converting celsius to Kelvint(K) = t ( o C) o C converting celsius to Kelvin Problems: 25 o C to K 300 K to o C

Specific Heat The quantity of heat required to raise one gram of a substance by one degree celsius.The quantity of heat required to raise one gram of a substance by one degree celsius. Metals tend to have low specific heats (What does having a low specific heat mean?)Metals tend to have low specific heats (What does having a low specific heat mean?) Water has a high specific heat! (Why does a watched pot never boil?)Water has a high specific heat! (Why does a watched pot never boil?) Specific heat is a characteristic property which means every substance has its own unique specific heat!Specific heat is a characteristic property which means every substance has its own unique specific heat!

Specific Heat Equation Cp = q.Cp = q. m. T Cp = specific heat (J/ g o C) (K) q = heat energy (J) m = mass (g) T = change in temp ( o C or K) T = change in temp ( o C or K)

Specific Heat Equation CpCp q mT