Do Now – April [5(6) – 1], What is the letter equation for a single- replacement reaction? 2.In complete sentences, compare/contrast endothermic and exothermic reactions.

Agenda Do Now/Announcements Get ready to feel it?!?! (the energy that is) Endo/Exo Lab! Work Time/Quiz Preparation Exit Ticket UNIT 5 QUIZ TOMORROW!

Objectives SWBAT observe and distinguish between endothermic and exothermic reactions using descriptions, equations, graphs, and a lab investigation.

Quick Question When potassium nitrate dissolves in water, the beaker containing the solution gets cooler. Is dissolving this salt an exothermic or an endothermic process? SHHH…DO NOT SHOUT OUT YOUR ANSWER Think about the answer to yourself for 15 seconds

Energy in Chemical Reaction If energy is a REACTANT, then it is being ADDED to the molecules This is an endothermic reaction If energy is a PRODUCT, then it is being RELEASED from the molecules This is an exothermic reaction

Practice Write each equation and then label the following them as endothermic or exothermic: 1.2 HCl kJ  H 2 + Cl NH O 2  4 NO + 6 H 2 O kJ 3.Cu + Cl 2  CuCl kJ 4.H 2 O + C kJ  CO 2 + 2H 2

Graphing Energy Changes A graphic way to show how energy is transferred during a reaction Potential Energy of Reactants { Potential Energy of Products }

P o t. e n er g y Reaction coord = potential energy of the reactants 2 = activation energy 3 = heat of reaction 4 = potential energy of the products = the potential energy of the activated complex

A B C 1.What represents the potential energy of the reactants? 2.What represents the potential energy of the products? 3.What represents the potential energy of the activated complex? 4.What represents the heat of reaction? 5.What represents the activation energy? 6.Is this reaction endothermic or exothermic? 7.What represents the activation energy of the reverse reaction?

Something you might see in college….

What Happens in a Chemical Reaction? To start a chemical reaction: –Need reactants (ingredients) –Often, need energy (activation energy) During a chemical reaction: –Molecules must come together in just the right way in order to react –The point at which the molecules have done exactly half of the change is referred to as the transition state At the end of a chemical reaction: –Formation of products –Energy change

Energy Graph Need-to-Knows! Activation energy (E a ) is the minimum amount of energy needed to make a reaction take place Transition state (T s ) is a temporary product that persists while old bonds are breaking and new bonds are forming (also known as activated complex) Heat of reaction (∆H) is the amount of energy change between the reactants and products (also called enthalpy of reaction)

Graphing Energy Changes Transition State aka Activated Complex

Energy Graph Practice Label each letter on the graph: See what you remember!

Graphing Energy Changes

Graphing Energy Changes Endo vs. Exo ΔH is positive!

Graphing Energy Changes Endo vs. Exo ΔH is negative!

Graphing Energy Changes Endo vs. Exo

Graphing Energy Changes Practice 1 Read the following reaction scenario and complete the following: 1.Write a balanced chemical equation 2.Label the reaction as endothermic or exothermic 3.Draw the correct energy diagram The combustion of the hydrocarbon glucose (C 6 H 12 O 6 ) produces carbon dioxide, water, and releases 2830 kJ.

Graphing Energy Changes Practice 2 Read the following reaction scenario and complete the following: 1.Write a balanced chemical equation 2.Label the reaction as endothermic or exothermic 3.Draw the correct energy diagram After absorbing 66.4 kJ of energy, 1 mole of nitrogen gas and 2 moles of oxygen gas react to form 2 moles of nitrogen monoxide.

Reaction Energy Foldable 1.Title Page 2.1 st Flap: Important definitions, descriptions, and characteristics –Explain how you would know if a reaction is endo/exothermic using such descriptions 3.2 nd Flap: Example equation for both an endothermic and exothermic reaction –Explain how you would know if a reaction is endo/exothermic using chemical equations 4.3 rd Flap: Example graph for each reaction –Explain how you would know if a reaction is endo/exothermic using energy graphs

Exit Ticket 1.What is chemical potential energy? 2.Draw a quick energy diagram for an endothermic reaction (just the shape – you do not need to label the parts!)

Heat of Reaction Heat is energy that flows from a warmer object to a cooler object (page 491)

Collision Theory The collision theory states that atoms, ions, and molecules must collide is order to react (page 532) CRASH!!!

How does HEAT relate to the COLLISION THEORY? More heat (higher temperature) means more collisions More collisions mean faster reaction Therefore, more heat means faster reaction Refrigerator vs. oven

Remember Reaction Rate? Reaction rate is how fast reactants turn into products Remember the Alka Selter demo??

Five Factors that Affect Reaction Rate 1.Reactivity of reactants 2.Concentration 3.Surface Area 4.Temperature 5.Catalyst

Reactivity of Reactants Some substances react more readily than others Calcium and sodium are both reactive metals; however, what happens when each is added to water is very different (page 536) The more reactive a substance, the faster the reaction rate

Concentration Concentration is a measure of the amount of a substance in a solution –How much stuff do you have? Reactions speed up when the concentrations of reacting particles increase (page 537)

Surface Area Surface area is how much exposed area an object has The greater the surface area, the more collisions, and the faster the reaction Grinding substance increases reaction rate Example: sugar cube vs. granular sugar (page 537)

Temperature Temperature is a measure of kinetic energy (collisions) (page 538) –Related to heat Generally, increasing temperature increases reaction rate If temperature increases, then… –Kinetic energy increases –Collisions increase –Reaction rate increases

Catalyst Increasing temperature is not always the best thing to do A catalyst is a substance that increases the reaction rate but is not involved in chemical reaction (page 539) Catalysts do not yield more product Catalysts are not written in chemical equations

Exit Ticket Read the following scenario and answer the questions below. Dr. Danger wants to react magnesium metal with water. He knows that magnesium is a very reactive metal. He decides to react the two reactants at 90 ºC and 60 ºC. At what temperature, will the reaction happen the fastest? What other factors could affect the reaction rate of Dr. Danger’s experiment?

ENERGY OF CHEMICAL REACTIONS Chemical reactions always involve a change in energy. Energy is neither created or destroyed. Energy is absorbed or released in chemical reactions. Chemical reactions can be described as endothermic or exothermic reactions. Endothermic Reactions Chemical reactions in which energy is absorbed are endothermic. Energy is required for the reaction to occur. The energy absorbed is often heat energy or electrical energy. Adding electrical energy to metal oxides can separate them into the pure metal and oxygen. Adding electrical energy to sodium chloride can cause the table salt to break into its original sodium and chlorine parts. Exothermic Reactions Chemical reactions in which energy is released are exothermic. The energy that is released was originally stored in the chemical bonds of the reactants. Often the heat given off causes the product(s) to feel hot. Any reaction that involves combustion (burning) is an exothermic chemical reaction. The next two pages include labs for both endothermic and exothermic reactions!