Unit 5 - Chemical reactions and balancing equations

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Physical Properties

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29 Terms

1

Physical Properties

Can be observed or measured without changing the composition of the matter

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2

Chemical Properties

a substance’s ability to undergo changes that transform it into a different substance

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3

Chemical reactions

The process by which substances interact to form new substances with different compositions

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4

Chemical change

A change in matter on a molecular level that produces one or more new substances

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5

Unexpected color change

New molecules created in a chemical reaction radiate light differently, producing new colors

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6

Rusting

A chemical reaction that causes rust called oxidation

<p><span>A </span><strong><span>chemical reaction</span></strong><span> that causes rust called </span><em><span>oxidation</span></em></p>
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7

Combustion reaction

A chemical reaction between substances, usually a hydrocarbon with oxygen, to produce CO2, water (H2O), light, and heat

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8

Precipitate forms

A chemical reaction that causes a solid suddenly appears in a solution and settles to the bottom, collects on another object, or makes the solution cloudy

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Bubbles form

When gases produced in a chemical reaction are released

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10

Temperature change

When the temp. increases, energy was released during a chemical reaction.

When the temp. decreases, energy was absorbed during a chemical reaction

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11

Change in Odor

when two or more compounds or elements are mixed and a scent or odor is present, a chemical reaction has taken place

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12

chemical equation

A representation of a chemical reaction using symbols and chemical formulas

<p><span>A representation of a chemical reaction using symbols and chemical formulas</span></p>
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13

reactants

The starting substances that are combined to make products

<p>The s<span>tarting substances that are combined to make products</span></p>
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products

the new substances which result from the chemical reaction

<p><span>the new substances which result from the chemical reaction</span></p>
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15

Chemical Formula

  • represents the composition of a molecule or compound. 

  • It lets you know how many of each atom there are. 

<ul><li><p>represents the composition of a molecule or compound.&nbsp;</p></li><li><p>It lets you know how many of each atom there are.&nbsp;</p></li></ul>
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<p>Reaction Symbols</p>

Reaction Symbols

The small symbols in the parentheses (s, l , g, aq)  next to each chemical formula indicate the state of matter of each substance in the reaction

<p>The small symbols in the parentheses (<em>s, l , g, aq) </em>&nbsp;next to each chemical formula indicate the <strong>state of matter </strong>of each substance in the reaction</p>
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17

Subscripts

Tells you the amount of atoms of an element in each molecule 

H2O ~ There are two hydrogen atoms in a water molecule 

<p>Tells you the amount of atoms of an element in each molecule&nbsp;</p><p><strong>H<span style="color: red"><sub>2</sub></span>O</strong> ~ <em>There are </em><strong><em><span style="color: red">two</span></em></strong><em> hydrogen atoms in a water molecule&nbsp;</em></p>
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Coefficients

tells you how many molecules of a substance there are 

3H2O ~ There are three water molecules, this means there are 6 total hydrogen atoms and 3 total oxygen atoms

<p>tells you how many molecules of a substance there are&nbsp;</p><p><strong><span style="color: red">3</span>H<sub>2</sub>O </strong>~<strong> </strong><em>There are </em><strong><em>three</em></strong><em> water molecules, this means there are </em><strong><em>6 total hydrogen atoms </em></strong><em>and </em><strong><em>3 total oxygen atoms</em></strong></p>
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19

The Law of Conservation of Mass

Mass is neither created nor destroyed during chemical or physical reactions

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Balancing Equations

The Law of Conservation of Mass is applied by balancing the number & type of atoms on either side of the equation

A balanced chemical equation has the same number of each type of atom on the product side and the reactant side

We change the coefficients of the molecules.

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21

Synthesis reactions

Two or more substances combine to form a new compound

A + BAB

Forming bonds releases energy (Exothermic)

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Decomposition reaction

A chemical reaction in which a single compound is broken down into 2+ smaller compounds

AB  —energyAB

Breaking bonds requires energy

<p>A chemical reaction in which a <strong>single</strong> compound is <strong>broken down</strong> into <strong>2+ </strong>smaller compounds</p><p><strong><span style="color: red">A</span><span style="color: blue">B</span></strong>&nbsp; —<em>energy</em>→ <strong><span style="color: red">A</span></strong> +&nbsp;<strong><span style="color: blue">B</span></strong></p><p>Breaking bonds requires energy</p>
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23

Single replacement/Single displacement reaction

When one element replaces a similar element in a compound

AX + BBXA

<p>When <strong>one</strong> element replaces a similar element in a compound</p><p><strong><span style="color: red">A</span><span style="color: green">X</span></strong> + <strong><span style="color: blue">B</span></strong> → <strong><span style="color: blue">B</span><span style="color: green">X</span></strong> +&nbsp;<strong><span style="color: red">A</span></strong></p>
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24

Double Displacement Reaction

Ions from two compounds in a solution exchange places to produce two new compounds

AB + CDAD + CB

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Signs of a Double Displacement Reaction

  • a precipitate that settles out of the solution, 

  • a gas that bubbles out of the solution, 

  • or a molecular compound (like water)

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26

Chemical energy

energy stored in the chemical bonds of a substance

Chemical reactions always involve energy changes

Making and breaking bonds involve energy changes

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27

Activation Energy

The energy required to break the bonds in the reactants for a chemical reaction to occur.

Must supply energy to break bonds!

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28

Endothermic

more thermal energy is ABSORBED  than released.

Endo = into

Surroundings feel COLD

REACTANTS  + ENERGY → PRODUCTS

REACTANTS + HEAT → PRODUCTS

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29

Exothermic

more thermal energy is RELEASED than absorbed

Exo = exit

Surroundings feel HOT

REACTANTS → PRODUCTS + ENERGY

REACTANTS → PRODUCTS + HEAT

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