Download Chemical Reactions

Chemical Reactions
Test on Friday April 19
Chemical Reaction
• Chemical Reaction – a change in which one
or more substances are converted into new
substances
• Reactants – substances that react
• Products – substances that are produced
Reactants  Products
Conservation of Mass
• Total mass of reactants is always equal to
the total mass of products – Antoine
Lavoisier
• Matter is not created or destroyed; it is
conserved.
• Law of Conservation of Mass
10 grams HgO = 0.7 grams O + 9.3 grams Hg
Father of Modern Chemistry
• Lavoisier is known as the Father of Modern
Chemistry for this work along with the work
he did on types of reactions
• Wrote a book called “Elements of
Chemistry” in 1790
• He developed the nomenclature we use
today to describe chemical compounds and
reactions.
Chemical Equations
• A way to describe a chemical reaction using
chemical formulas and other symbols.
•  produces or forms
• + plus
• (s) solid (l) liquid (g) gas (aq) aqueous
Coefficients
• Coefficients – the numbers in front of the
chemical formulas that represent the
number of units of each substance taking
part in a reaction.
• Must be whole numbers
• Act like a multiplier and apply to the entire
formula
• Subscripts – small numbers that tell how
many atoms a particular molecule has
Sample Equations
• 2Hg + Br2 → Hg2Br2
• Hg2Br2 + 2Cl2 → 2HgCl2 + Br2
• 2C4H10 + 13O2 → 8CO2 + 10H2O
Balanced Chemical Equations
• An equation is balanced if it has the same
number of atoms on each side of the
equation.
• This is due to the Law of Conservation of
Matter: Matter cannot be created or
destroyed.
Steps to Balancing
• Write a chemical equation if you don’t
already have one.
– Remember Oxygen, Chlorine and Hydrogen are
diatomic.
• Count the atoms on each side.
• Choose coefficients that multiply to balance
the equation.
• Recheck the numbers.
Types of Reactions
• There are 5 types of reactions:
– Combustion
– Synthesis
– Decomposition
– Single Displacement
– Double Displacement
Combustion Reactions
• When a substance reacts with oxygen to
produce energy in the form of heat and light
(fire)
• Only includes the elements: C, H, and O
• Always produces CO2 and H2O
CxHx + O2  CO2 + H2O
Synthesis Reactions
• Two or more substances (elements)
combine to form one substance (molecule)
• Easily found because there is only one
product
Element + Element  Molecule
Decomposition Reaction
• One substance (molecule) breaks down into
multiple substances (elements)
• Easily found because there is only one
reactant.
Molecule  Element + Element
Single Displacement
• An element reacts with a molecule. One of
the elements in the molecule recombines
with the original element.
• The reactants and products are both one
element and one molecule.
A + BC  AC + B
“unhappy breakup”
Double Displacement
• The positive ions switch places to form two
new compounds.
• The reactants and products are always two
molecules.
AD + BC  AC + BD
“happy breakup”
Activity Series
• The Activity Series is a chart that tells which
metals will replace other metals in a
reaction.
Vocabulary
• Precipitate – insoluble compound that
comes out of a solution
• Oxidation – loss of electrons
• Reduction – gain of electrons
Chemical Reactions and Energy
• All chemical reactions either absorb or
release energy
• Breaking bonds requires energy
• Forming bonds releases energy
• Energy can take the form of light, heat,
sound, or electricity.
Exergonic
• Reactions that release energy are called
Exergonic
• When that energy is given off as heat its
called Exothermic
– You can feel the reaction get warmer.
Endergonic
• Reactions that absorb energy are called
Endergonic.
• When that energy is in the form of heat its
called Endothermic.
– You can feel the reaction get colder.
Catalysts and Inhibitors
• A catalyst is a substance that speeds up a
reaction.
• An inhibitor is a substance used to slow
down a reaction or prevent it completely.
• The catalyst and the inhibitor do not
participate in the reaction. They remain
unchanged after the reaction is over.