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.