Agenda: 3/27• Objective: to predict products in a chemical reaction

• Warm-up: Formative Assessment

• Chemical Reactions

Objective: To predict what a chemical reaction will produce

•What will we learn?

• Balancing equations • Types of reactions • When reactions will take place

Objective: To predict what a chemical reaction will produce

•What do we need to know?

• Names and formulas• Indicators of chemical change • Moles

CHEMICAL REACTIONS

Reactants: Zn + I2 Product: Zn I2

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What are the indicators that there is a chemical reaction?

What is a chemical reaction?

• Atoms are combined into compounds or separated and then rearranged.

• New substances must be formed• New physical and chemical properties

• Energy is always involved

Notes: 1. Chemical Reactions• Process in which substances (reactants) change into

1 or more different substances (products)

Reactants → Products

Yields

Products have different physical and chemical properties than the reactants.

Explain why in your notes:

Notes: Energy is always involved:

- In exothermic reactions, energy is released.

- In endothermic reactions, energy is added (absorbed)

Energy change (∆H = change in heat) is shown 2 ways:

Exothermic: ∆H = - or shown as a product

Endothermic: ∆H= + or shown as a reactant

Notes: Chemical Change must take place.

• Indicators of chemical change:

1: change in temperature

2: producing bubbles (gas) without boiling

3: change in color

4: a precipitate is formed (solid from 2 liquids)

Introduction: Chemical EquationsTheir Job: Way to represent the relative amounts of reactants and products and their relative amounts in a reaction.

4 Al (s) + 3 O2 (g) ---> 2 Al2O3 (s)

The numbers in the front are called coefficients.

____________The letters (s), (g), and (l) are the physical states of compounds.

Word Equation for the reaction:The carbon reacts with oxygen to yield carbon dioxide.Chemical equation: C + O2 CO2

This contains the same information as the English sentence but has quantitative meaning as well.

The charcoal used in a grill isbasically carbon.

Notes: Chemical Equations• Way to represent the relative amounts of reactant and

product. (A recipe)

• Satisfies the Law of Conservation of Matter (Mass)

Atoms are not created nor destroyed in a chemical reaction (just re-arranged)

Mass is neither created nor destroyed in a chemical reaction.

There must be the same amount of mass on the product side (after the reaction) as the reactant side (before the reaction.)

• Solid ___• Liquid ____• Gas ___• Aqueous solution (aq)• Reversible reactions• Reactants are heated

• Catalyst H2SO4

• Escaping gas ()

Notes: Symbols Used in Equations

Because of the principle of the conservation of matter,

an equation must be balanced.

It must have the same number of atoms of the same kind on both sides.

Introduction: Chemical Equations

Lavoisier, 1788

BALANCING CHEMICAL REACTIONS

Balancing EquationsBalancing Equations

___ Al(s) + ___ Br2(l) ---> ___ Al2Br6(s)

• When balancing a chemical reaction Coefficients are added in front of a compounds to balance the reaction, but

you may not change the subscripts.

• Changing the subscripts changes the compound.

Important in Balancing Equations

Subscripts vs. Coefficients

• The subscripts shows: ?

• The coefficient shows: ?

Why balance chemical reactions?• Law of Conservation of Matter:

• matter is neither created nor destroyed in __ ________ _________.

• In a chemical reaction, atoms are combined, separated and/or rearranged.

• Not atoms are lost or gained in a chemical reaction.

In a balanced reaction• Chemical reactions are shown with symbols (formulas in

an equation) • Starting materials = reactants • Produces, yields = arrow• End materials = products

• # atoms of reactants= # atoms of products

Steps to balance equations:• Start with correct formulas for the compounds.

• Never, never change the formula (subscripts) • Put a box around the formulas as a reminder.

• Count how many atoms of each type of element on each side of the equation.

• Use multipliers (called coefficients) in front of the formulas on each side of the equation until the number on each side matches up.

Notes: Methane and oxygen produces carbon dioxide and water.1. Correct formulas and symbols.• Put box around each formula.

2. Count the number of atoms on both sides of the equation

Methane + oxygen carbon dioxide + water

Notes: Methane and oxygen produces carbon dioxide and water.3. Balance the equation using coefficients.(Coefficients are multipliers in front of the compounds)

4. Use the smallest whole number possible.

Examples: • Copper and silver (I) nitrate combine to yield copper (II)

nitrate and silver.

Examples• The reactants magnesium and aluminum chloride produce

aluminum and magnesium chloride.

Examples for your notes: • Carbon reacts with oxygen to produce carbon dioxide.

Practice balancing equations• ____ Ca + ____ O₂ ____ CaO

• ____ Br₂ + ____ LiF ____ LiBr + ____ F₂

• ____ V + ____ ZnBr₂ ____ VBr₃ + ____ Zn

• ____ Li + ____ Pb(OH)₂ ____ Pb + ____ LiOH

• ____ C₄H₈ + ____ O₂ ____ CO₂ + ____ H₂O

• ____ Ga(OH)₃ + ____ KF ____ KOH + ____ GaF₃

Chemical EquationsChemical Equations4 Al(s) + 3 O2(g) ---> 2 Al2O3(s)

This equation means

4 Al atoms + 3 O2 molecules ---produces--->

2 molecules of Al2O3

AND/OR

4 moles of Al + 3 moles of O2 ---produces--->

2 moles of Al2O3

Balancing EquationsBalancing Equations

____C3H8(g) + _____ O2(g) ---->

_____CO2(g) + _____ H2O(g)

____B4H10(g) + _____ O2(g) ---->

___ B2O3(g) + _____ H2O(g)

Balancing EquationsBalancing EquationsSodium phosphate + iron (III) oxide sodium oxide +

iron (III) phosphate

Na3PO4 + Fe2O3 ---->

Na2O + FePO4

____ P + O2 → P4O10 ____ Mg + O2 → MgO

____ HgO → Hg + O2 ____ Al2O3 → Al + O2

____ Cl2 + NaBr → NaCl + Br2 ____ H2 + N2 → NH3

Balancing chemical reactions

____ Na + Br2 → NaBr ____ CuCl2 + H2S → CuS + HCl 

____ HgO + Cl2 → HgCl + O2 ____ C + H2 → CH4

 

____ KClO3  →   KCl  +  O2  ____ S8 + F2 → SF6

 

____ BaCl2   +   Na2 SO4 →     NaCl   +   BaSO4