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

10 grams HgO = 0.7 grams O + 9.3 grams Hg 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

Element + Element  Molecule 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.