Chemical Reactions Ms. Samayoa Created by Kesler Science – More 5E lessons at KeslerScience.com Ms. Samayoa

Learning Objectives: Students will be able to identify the reactants and products in a chemical reaction.

Academic Vocabulary Subscript, coefficient, products, reactants, law of conservation of mass

CHEMICAL REACTIONS A chemical reaction is a chemical change that occurs when two or more substances combine to form a new substance

Physical change vs chemical reaction In order to further understand chemical reactions, we need to be able to differentiate between physical and chemical changes

EVIDENCE OF PHYSICAL CHANGE Phase Changes Sublimation, deposition, evaporation, condensation, melting, and freezing Dissolving Cutting Bending

CHECK FOR UNDERSTANDING In your notes, give one example of a physical change and list the evidence Be prepared to be called on by Ms. Samayoa

EVIDENCE OF CHEMICAL CHANGE Color change Smell New matter created (precipitation) Gas created (bubbles) Heat or light created

CHECK FOR UNDERSTANDING In your notes, give one example of a chemical change and list the evidence Be prepared to be called on by Ms. Samayoa

Is it a chemical reaction? Write down any observations that you see in Ms. Samayoa’s demonstration Afterwards, with a partner, answer the following question: Was the demonstration an example of a chemical reaction? © KeslerScience.com

Was it a chemical reaction? The answer is YES! There was a chemical reaction! The heat from the fire allowed enough energy for the alcohol to react with the oxygen found in the air to convert it to carbon dioxide and water 2C3H8O + 9O2  6CO2 + 8H2O © KeslerScience.com

Scientific Explanation The scientific explanation is that rubbing alcohol is made out of 70% alcohol and 30% water Water has a high heat capacity which means it can absorb a lot of heat In this case, water is absorbing all the heat from the flame, preventing the flame from burning the dollar bill © KeslerScience.com

2 H2O Review Balancing Chemical Equations Subscripts describe the # of atoms in a molecule H2O Model The Coefficient represents the number of molecules 2 Molecules of H2O 2 H2O H O H O Emphasize the difference between subscripts and coefficients © KeslerScience.com

Check for Understanding Molecule Number of Each Atom Total Atoms 2KClO3 K= Cl= O= Total Atoms= 6H2O O= H= 4Al2O3 Al= O= 2C6H8O7 C= H= O= 6Na3C6H5O7 Na= C= H= O= © KeslerScience.com

2H2 + O2  2 H2O Chemical Equation Balancing Chemical Equations Broken into 3 main parts Reactants Arrow = Chemical Reaction Products RAP is an easy way to remember. 2H2 + O2  2 H2O Reactants Product Arrow © KeslerScience.com

2H2 + O2  2 H2O Reactants Balancing Chemical Equations Elements or compounds which exist BEFORE a chemical reaction 2H2 + O2  2 H2O Reactants Students should take these notes on the INB template. © KeslerScience.com

2H2 + O2  2 H2O Products Balancing Chemical Equations New substances that are created by the rearranging of atoms AFTER a chemical reaction 2H2 + O2  2 H2O Product © KeslerScience.com

2H2 + O2  2 H2O Arrow/Chemical Reaction Balancing Chemical Equations The arrow represents a chemical reaction. In a chemical reaction, atoms are rearranged to form new substances In a chemical reaction, atoms are not lost or gained; they must be equal on both sides 2H2 + O2  2 H2O Arrow © KeslerScience.com

Check for Understanding 6CO2 (g) + 6H2O (l)  C6H12O6 (s)+ 6O2 (g) Work with a partner to find the following items: List the Products List the Reactants What does the arrow Represent? Answers: C6H12O6 and O2 CO2 and H2O Chemical reaction or chemical change 18 12 © KeslerScience.com

(s) solid (g) gas (l) liquid (aq) aqueous Phase States It is also important to know the phase (state) of the reactants and products in a chemical reaction To show these phases in the reaction, you will use the subscripts: (s) solid (l) liquid (g) gas (aq) aqueous

Check for Understanding 6CO2 (g) + 6H2O (l)  C6H12O6 (s)+ 6O2 (g) Work with a partner to find the following items: What are the phase states of the reactants? What are the phase states of the products? Answers: C6H12O6 and O2 CO2 and H2O Chemical reaction or chemical change 18 12 © KeslerScience.com

Law of Conservation of Mass Balancing Chemical Equations Law of Conservation of Mass Matter (atoms) can neither be created  nor destroyed. Atoms can only be rearranged. © KeslerScience.com

Balancing Chemical Equations Equal number of the same type of atom on each side. If unbalanced, you can only change the coefficient to make it balanced. You CANNOT change subscripts. © KeslerScience.com

Check for Understanding © KeslerScience.com

2 Ag2O g Ag + O2 4 2 Balanced! Balancing Chemical Equations Practice Step 1 – Take Inventory of the elements and atoms on the product and reactant side. Step 2 – Is it balanced? Step 3 – If unbalanced, change coefficients until it’s balanced. 2 Ag2O g Ag + O2 4 2 Ag : 2 O : 1 4 Ag : 1 O : 2 4 2 2 As of 2016 the Texas standards says student are to “recognize if a chemical equation is balanced using coefficients”. For your on-level classes you could stop here. It’s either balanced or it isn’t. For your advanced classes you could actually teach them how to balance the equation. Balanced! © KeslerScience.com

CH4 + Cl2  CCl4 + HCl 4 4 Balanced! Balancing Chemical Equations Practice Step 1 – Take Inventory of the elements and atoms on the product and reactant side. Step 2 – Is it balanced? Step 3 – If unbalanced, change coefficients until it’s balanced. CH4 + Cl2  CCl4 + HCl 4 4 C : 1 H : 4 Cl : 2 C : 1 H : 1 Cl : 5 4 8 8 As of 2016 the Texas standards says student are to “recognize if a chemical equation is balanced using coefficients”. For your on-level classes you could stop here. It’s either balanced or it isn’t. For your advanced classes you could actually teach them how to balance the equation. Balanced! © KeslerScience.com

Check for Understanding – Balance the Equation Step 1 – Take Inventory of the elements and atoms on the product and reactant side. Step 2 – Is it balanced? Step 3 – If unbalanced, change coefficients until it’s balanced. NaBr + CaF2  NaF + CaBr2 Allow students to work with a partner Answer: 2NaBr +CaF2  2NaF + CaBr2 © KeslerScience.com

Check for Understanding – INB Template I would only do this sheet in your advanced class unless you have to teach HOW to balance equations rather than determining if it is balanced or not.

Check for Understanding Can you… Recognize whether a chemical equation balanced or not? Relate balanced equations to the law of conservation of mass. Clear up any confusion and answer questions. © KeslerScience.com