Chemical Reactions Chapter 7 Are you into them?

7.1 Describing Reactions

Equations Represent Reactions Reactant  Product 2H 2 + O 2  2H 2 O (Coefficients show molar ratios)

The Law of Conservation of Mass In any chemical reaction, the final mass of the products ALWAYS equals the original mass of the reactants. In other words – in a chemical reaction, mass cannot be added or gained. The atoms on one side of the equation MUST balance with the atoms on the other side of the equation! For example: Na(s) + Cl 2 (g)  NaCl(s)

Na(s) + Cl 2 (g)  NaCl(s) In this case we can add a coefficient Coefficient means a number in front of the molecule. This number is then multiplied by the subscript (indicating # of atoms).

Examples 1. ________ Cl 2 (g) + _________ NaBr (aq)  _________ Br 2 (l) + _________ NaCl(aq) 2. ________ Cr 2 O 3 (s)  _________ Cr(s) + __________ O 2 (g) 3. _______ H 3 PO 4 (aq) + _______ NaOH(aq)  _______ Na 3 PO 4 (aq) + _______ HOH(l) 4._______ C 2 H 4 (g) + _______ O 2 (g)  ________ CO 2 (g) + ________ H 2 O(g) 5. ________ Ca(OH) 2 (s) + _______ HCl(aq)  ________ CaCl 2 (aq) + ________ HOH(l) 6. _______ CoCl 2 (aq) + ______ NH 4 NO 3 (aq)  _______ Co(NO 3 ) 2 (aq) + ______NH 4 Cl(aq) 7. ________ C 6 H 14 (g) + _________ O 2 (g)  __________ CO 2 (g) + _________ H 2 O(g)

Examples 1. ________ Cl 2 (g) + _________ NaBr (aq)  _________ Br 2 (l) + _________ NaCl(aq) 2. ________ Cr 2 O 3 (s)  _________ Cr(s) + __________ O 2 (g) 4._______ C 2 H 4 (g) + _______ O 2 (g)  ________ CO 2 (g) + ________ H 2 O(g) 5. ________ Ca(OH) 2 (s) + _______ HCl(aq)  ________ CaCl 2 (aq) + ________ H 2 O(l) Challenge! 5. ________ C 6 H 14 (g) + _________ O 2 (g)  __________ CO 2 (g) + _________ H 2 O(g) 6. _______ CoCl 2 (aq) + ______ NH 4 NO 3 (aq)  _______ Co(NO 3 ) 2 (aq) + ______NH 4 Cl(aq)

Remember! In order to show that the mass is conserved during a reaction, a chemical equation must be balanced!

…Tricks to Balancing Every atom MUST be balanced Start with polyatomic ions that appear only once on each side Leave H 2 and O 2 and other single element molecules until the end Do not split up polyatomic ions into separate elements – keep them intact (example: PO 4 – keep P and 4 O together – notice that on the other side of the equation it is also intact) Write water as HOH – it’s easier to balance with hydroxide (OH) Do not use fractions – and make sure your final coefficients are in the LOWEST terms When balancing combustion reactions, notice that oxygen appears twice on the product’s side (CO 2 and H 2 O – the coefficient in front of the H 2 O MUST be an even number – or you will not be able to balance the O 2 on the reactant’s side Balance in pencil!! Check your final equation – atoms must be equal on both sides of equation

Speed Dating!

Date 1 Hello, my name is __________________. 1 st person – give answer 2 nd person – explain why it is the right answer Write it down.

Date 2 Hello, my name is __________________. (write your date’s name on your answer sheet) 1 st person – give answer 2 nd person – explain why it is the right answer and the others are wrong Write it down. Explain.

Date 3 Hello, my name is __________________. (write your date’s name on your answer sheet) 1 st person – give answer 2 nd person – explain why it is the right answer and the others are wrong Write it down. Explain.

Date 4 Hello, my name is __________________. (write your date’s name on your answer sheet) 1 st person – give answer 2 nd person – explain why it is the right answer and the others are wrong Write it down. Explain.

Date 5 Hello, my name is __________________. (write your date’s name on your answer sheet) 1 st person – give answer 2 nd person – explain why it is the right answer Write it down. Explain

Date 6: Feedback  No Names! 1. Hello, my name is __________________. (write your date’s name on your answer sheet) 2. What was your favorite date? What made it good? 3. What was something you thought could be done better in some of your “dates”?

Counting with Moles Similar concept: 1 dozen = 12 …in Chemistry  1 mole = a lot. – Specifically: 6.02 X AKA: Avogadro’s Number Get it? How many atoms of Iron are in 1 mole of Fe?

Molar Mass The mass of 6.02 X Particles – Particles = general term for element/molecule/compound. Molar mass is the mass of 1 mol. of whatever… Atomic mass # = mass in amu = molar mass in grams – Also the molar mass of 1 mol. of that element in grams Try this: What is the molar mass of O 2 ?

Practice Was the mass conserved?

Molar Mass Calculation Practice Answers

Manipulating Moles Practice Formula to Molar Mass (g) – Calculate the molar mass of Al(NO 3 ) 3 How many moles of Al(NO 3 ) 3 is that? Grams to Moles – If I have 639g of Al(NO 3 ) 3, how many moles do I have? Moles to Grams – What is the mass (g) of 5 moles of Al(NO 3 ) 3 ? Resources/Help Videos

7.2 Types of ReactionsTypes of Reactions

4 Types Of Reactions In chemistry there are millions of chemical reactions. But most reactions can be classified as one of 4 types: Synthesis: A + B -> AB Decomposition: AB -> A + B Single Replacement: A + BC -> AC + B Double Replacement: AB + CD -> AD + CB Here is a short explanation and examples of each type of reaction.

Type 1: Synthesis (Composition) In a synthesis reaction (also known as a composition reaction), two substances combine to form a larger substance. Analogy: boy A walks into the dance, sees girl B and ask her to dance. They then form couple AB. Synthesis: A + B -> AB

Here are four synthesis reactions: Hydrogen + oxygen yields water 2H 2 + O 2 -> 2H 2 O Magnesium + nitrogen yields magnesium nitride 3Mg + N 2 -> Mg 3 N 2 Iron + sulfur yields iron(II) sulfide Fe + S -> FeS Sodium + phosphorus yields sodium phosphide 3Na + P -> Na 3 P Simplest Type Of Synthesis Reaction = two elements combine to form a compound

Side Note: Diatomic Atoms The diatomic elements are: hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine and iodine. As elements they always travel in pairs of atoms and therefore you must write then as: H 2 N 2 O 2 F 2 Cl 2 Br 2 and I 2

Type 2: Decomposition In a decomposition reaction, a larger substance breaks apart and forms two or more simpler substances. Dancers Analogy: boy A steps on girl B's toe. She gets upset and walks away.

Type 3: Single Replacement In a single replacement reaction, a more active element replaces a less active element in a compound. Analogy…

Example If fluorine gas is bubbled through a solution of potassium chloride, the fluorine will replace the chlorine. 2KCl + F 2 --> 2KF + Cl 2

Type 4: Double Replacement In a double replacement reaction, two metal ions (cations -in aqueous compounds) switch places. Analogy of dancers: Two couples are dancing. The two girls look over and state they wish to switch partners. And so...they do.

Double Replacement Examples

Combustion Reaction Rapid Reaction with Oxygen Produces light and heat. Anyone feeling cold today? ___C 2 H 6 O + ___O 2  ___H 2 O + ___CO 2

Oxidation-Reduction Reaction = RedoxRedox Reaction where an element loses electrons Electrons are transferred from one reactant to another. Fe 2 O 3 (s) + 2Al(s) Al 2 O 3 (s) + 2Fe(l) Loses electron = oxidation, reactant is oxidized Gaines electrons = reduction, reactant is reduced

7.4 Reaction Rates What would affect the rate of a chemical reaction?

Factors that Affect Reaction Rate Temperature Surface Area Concentration Stirring Catalysts

7.3 Energy Changes in Reaction Energy is either released or absorbed in reactions Chemical Bonds are either broken or formed

Law of Conservation of Energy Total amount of energy before and after is the same

Endothermic vs. Exothermic Endo – in Exo – out -therm – thermal energy Endothermic – net gain of energy - absorbs – More energy is required to break the bonds, than is released when the products form. Exothermic – net loss of energy - releases – More energy is released as the products form is less than the energy required to break the bonds in the reactants.