Endothermic and Exothermic Reactions 3_6: Chemical Energy Endothermic and Exothermic Reactions

Al + HCl  AlCl3 + H2 K + Fe2(SO4)3  K2SO4 + Fe Do Now Balance the reactions below: Al + HCl  AlCl3 + H2 K + Fe2(SO4)3  K2SO4 + Fe

2Al + 6HCl  2AlCl3 + 3H2 6K + Fe2(SO4)3  3K2SO4 + 2Fe Do Now Balance the reactions below: 2Al + 6HCl  2AlCl3 + 3H2 6K + Fe2(SO4)3  3K2SO4 + 2Fe

Objective I can determine whether a chemical reaction is endothermic or exothermic and draw an energy diagram for the reaction in a lab setting.

Agenda Do Now, Objective Vocabulary Mini-Labs Demo Lab Introduction to Energy Diagrams

Vocabulary There are 2 types of chemical reactions. Those that ABSORB energy, and those that GENERATE energy.

Endothermic Reaction Endothermic reactions ABSORB energy/heat from their surroundings. When endothermic reactions occur, it makes the surroundings COLDER. Students need to write down the definition for ‘endothermic reaction’

Exothermic Reaction Exothermic reactions RELEASE energy/heat to their surroundings. When exothermic reactions occur, it makes the surroundings HOTTER. Students need to write down the definition for ‘endothermic reaction’

Mini-Labs Working in groups of 3 you will observe an endothermic and an exothermic chemical reaction Follow ALL directions Write down your observations in the ‘lab’ section of your binder Obey lab safety rules

Mini-Lab 1: Ammonium Nitrate & Water Find the bag with small, white, pellets in it (10 g) Add 20 mL of water to the bag and seal it Observe what happens! Pour the contents of your bag down the drain with the water running Rinse out the plastic bag Throw away the plastic bag Write down your observations in the ‘lab’ section of your binder

Mini-Lab 2: Calcium Chloride OR Sodium Carbonate & Water Find the bag with white crystals in it (20 g) Add 20 mL of water to the bag and seal it Observe what happens! Pour the contents of your bag down the drain with the water running Rinse out the plastic bag Throw away the plastic bag Write down your observations in the ‘lab’ section of your binder

Ammonium nitrate and water NH4NO3 (s)   →   NH4+ (aq) + NO3-(aq) Ammonium nitrate dissociates (dissolves) in water to form the ions ammonium and nitrate. ENDOTHERMIC REACTION (absorbs heat) This is the reaction that is used in ‘instant’ cold packs from first aid kits.

Calcium chloride and water CaCl2 (s)   →   Ca2+ (aq) + Cl-(aq) Calcium chloride dissociates (dissolves) in water to form the ions Ca2+ and Cl-. EXOTHERMIC REACTION (releases heat) This is the reaction that is used in ‘instant’ hot packs from first aid kits.

Ba(OH)2*8H2O(s) + 2NH4SCN(s)  Ba(SCN)2(aq) + 2NH3(g) + 10H2O(l) Demo Lab This reaction occurs between ammonium thiocyanate and barium hydroxide Ba(OH)2*8H2O(s) + 2NH4SCN(s)  Ba(SCN)2(aq) + 2NH3(g) + 10H2O(l) ENDOTHERMIC reaction When the reaction occurs, heat is absorbed and the surroundings get colder, causing the ice to freeze

Day 2 – 96 minutes Goals Students can define endothermic, exothermic, activation energy, and change of enthalpy Students can draw potential energy diagrams for endothermic and exothermic reactions

Do Now What type of chemical reaction absorbs energy and requires energy for the reaction to occur? What type of chemical reaction generates (makes) energy and requires energy for the reaction to occur?

Do Now What type of chemical reaction absorbs energy and requires energy for the reaction to occur? ENDOTHERMIC REACTION What type of chemical reaction generates (makes) energy and requires energy for the reaction to occur? EXOTHERMIC REACTION

Al + HCl  AlCl3 + H2 K + Fe2(SO4)3  K2SO4 + Fe Do Now Balance the reactions below: Al + HCl  AlCl3 + H2 K + Fe2(SO4)3  K2SO4 + Fe

2Al + 6HCl  2AlCl3 + 3H2 6K + Fe2(SO4)3  3K2SO4 + 2Fe Do Now Balance the reactions below: 2Al + 6HCl  2AlCl3 + 3H2 6K + Fe2(SO4)3  3K2SO4 + 2Fe

Objective I can determine whether a chemical reaction is endothermic or exothermic by analyzing potential energy diagrams.

Agenda Do Now, Objective Vocabulary Review Potential Energy Diagrams Guided Reading Chem Review Questions Weekly Quiz

Endothermic Reaction Endothermic reactions ABSORB energy/heat from their surroundings. When endothermic reactions occur, it makes the surroundings COLDER. Students need to write down the definition for ‘endothermic reaction’

Examples of Endothermic Reactions Cooking an egg Melting ice Splitting a gas molecule apart Photosynthesis sunlight + 6CO2 + H2O = C6H12O6 + 6O2

Exothermic Reaction Exothermic reactions RELEASE energy/heat to their surroundings. When exothermic reactions occur, it makes the surroundings HOTTER. Students need to write down the definition for ‘endothermic reaction’

Exothermic Chemical Reaction Examples Combustion of fireworks Burning of natural gas 2H2 + O2 → 2H2O + heat

Guided Practice Which change is exothermic? freezing of water melting of iron vaporization of ethanol sublimation of iodine Why? Heat is released as molecules slow down going from a liquid to a solid

Guided Practice Which of the following changes is endothermic? freezing of water A candle flame Dissolving ammonium nitrate Baking bread Why? The bread dough must absorb energy before it will bake.

Vocabulary Activation Energy (Ea): The minimum energy required to start a chemical reaction Change in Enthalpy (ΔH): The change in energy in a system that undergoes (has) a chemical reaction). Also called the ‘heat of reaction’. Measure in kJ. +ΔH = the reaction absorbs energy  endothermic -ΔH = the reaction releases energy (fire!)  exothermic

Endothermic Reaction Potential Energy (kJ) Transition state Potential Energy (kJ) +ΔH = endothermic reaction Heat is absorbed during the reaction, this is why there is MORE potential energy at the end of the reaction, than at the beginning

Exothermic Reaction Potential Energy (kJ) Transition state reactants Potential Energy (kJ) This is a potential energy diagram P.E. stands for potential energy -ΔH = exothermic reaction products Heat is released from the reaction, this is why there is LESS potential energy at the end of the reaction, than at the beginning

Guided Practice Which of the following potential energy diagrams represent: A endothermic reaction?   An exothermic reaction?

Guided Practice Which of the following potential energy diagrams represent: A endothermic reaction?  C An exothermic reaction? A

Guided Practice Which statement correctly describes an endothermic chemical reaction? The products have higher potential energy than the reactants, and the H is negative. The products have higher potential energy than the reactants, and the H is positive. The products have lower potential energy than the reactants, and the H is negative. The products have lower potential energy than the reactants, and the H is positive.

Guided Practice Given the balanced equation: Which phrase best describes this reaction? endothermic with H = +1640 kJ endothermic with H = -1640 kJ exothermic with H = +1640 kJ exothermic with H= -1640 kJ

S(s) + O2 (g)  SO2 (g) + energy Guided Practice Given the following reaction: S(s) + O2 (g)  SO2 (g) + energy Is the reaction endothermic or exothermic? Exothermic

Guided Reading Complete the guided reading with a partner making sure to answer ALL questions Voices @ a whisper

Chem Review Questions – Writing Identify the following changes as endothermic or exothermic. (Hint: ask yourself whether the reaction requires the addition of heat energy to occur or does it release energy in the form of heat). Melting ice Lighting a match Dry ice subliming into carbon dioxide gas Frying an egg Burning gasoline Explosion of hydrogen gas when it reacts with oxygen gas

Chem Review Questions Melting ice – endothermic Lighting a match – endothermic, the reaction requires the addition of energy to raise the energy level of the reactants to the point where the reaction begins, and can continue without further energy input Dry ice subliming into carbon dioxide gas – endothermic, it has to absorb energy to warm up Frying an egg – endothermic, energy must be supplied to the egg in order to start the reactions and cook it until adequately fried Burning gasoline – exothermic, energy is released and powers the car Explosion of hydrogen gas when it reacts with oxygen gas - exothermic

Weekly Quiz Silently complete your quiz. When you are finished, turn it in and quietly put away your materials. GOOD LUCK!

C6H4Cl2(solid) + energy  C6H4Cl2(gas) Which process is exothermic Boiling of water Melting of copper Vaporization of CO2 Freezing of ice Given the balanced equation representing a phase change: C6H4Cl2(solid) + energy  C6H4Cl2(gas) It is endothermic and heat is released It is exothermic and heat is released It is endothermic and heat is absorbed It is exothermic and heat is absorbed

Compare and contrast endothermic and exothermic reactions Compare and contrast endothermic and exothermic reactions. Make sure your answer includes the word energy. 2H2O2  2H2O + O2. Identify the type of chemical reaction represented by the balanced reaction (synth, decomp, single replacement, etc.)

Balance Zn + HCl  H2 + ZnCl2 Which equation represents a decomposition reaction? CaCO3  CaO + CO2 Cu + 2AgNO3  2Ag + Cu(NO3)2 2H2 + O2  2H2O KOH + HCl  KCl + H2O