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.