Chemical Reactions

7.1 DESCRIBING REACTIONS

Changes in Substances Physical change – altered appearance but same composition  Water to steam  Glass bottle to broken glass Chemical change or reaction – results in a different chemical composition  Coal to ashes  Milk to sour milk

+ CoalOxygen Carbon Dioxide Chemical Reaction ReactantsProducts C + O 2 CO 2 (Solid) (Gas) (Gas)

+ Hydrogen Oxygen Water Chemical Reaction ReactantsProducts 2H + O 2 H 2 O (Gas) (Gas) (Liquid) +

Chemical Reactions Chemical reaction: rearranging chemical bonds of substances to form a different substance Show with chemical equation Reactant(s) Product(s) Coefficients show the amount of each item 2H 2 + O 2 2H 2 O

Law of Conservation Atoms are not created or destroyed during a chemical reaction All of the reactant atoms have to be in the product Not Correct: H 2 + O 2 H 2 O (two) (one) Correct: 2H 2 + O 2 2H 2 O (four) (two) (four) (two)

+ Chemical Reaction + CH 4 + O 2 CO 2 + H 2 O22 Balanced!

Law of Conservation In a chemical reaction, energy is not created nor destroyed but can change between chemical energy (in a chemical bond) and heat energy

Moles Mole – a unit like a dozen  Dozen = 12 items  Mole = 6.02 X items Mole of the element Na contains 6.02 X Na atoms Mole of CO 2 contains 6.02 X molecules of O=C=O

Moles in Chemistry I help you get the right amount of reactants for your chemical reaction.

Moles in Chemistry A chemical mole is something pest-y like me! Mole – unit that contains 6.02 X items.

Moles 3 H 2 + N 2 2 NH 3 you need 3 moles of hydrogen and 1 mole of nitrogen to make 2 moles of ammonia gas with no reactants left over amu of H 2 is 2 so 1 mole mass of H is 2 grams and 3 moles of H is 6 grams amu of N is X 2 so 1 mole of N is grams of nitrogen amu of NH 3 is (3 x1) = so 1 mole of NH 3 is grams; 2 moles is grams 6 g of H g of N g of NH 3

Moles Moles of elements in a compound: H 2 O requires two H for every one O so 2 moles of H atoms and one mole of O atoms makes one mole of H 2 O 3 H 2 + N 2 2 NH 3 (balanced chemical equation) : : you need 3 moles of hydrogen and 1 mole of nitrogen to make 2 moles of ammonia gas with no reactants left over (fastest reaction)

Moles in Chemistry How do you get a mole in chemistry! 1 mole mass = ___ grams ___ = substance’s amu

7. 2 TYPES OF REACTIONS

Types of Chemical Reactions Synthesis: A + B C (requires energy input) Decomposition: DE D + E (releases energy) Replacement JL+ HK LH+JK Oxidation/Reduction = loss/gain of e -  Oxidation: lose by gaining an O or losing a H  Reduction: gain by gaining a H or losing an O

Reversible Reactions Important chemical reaction in the body CO 2 + H 2 0 H 2 CO 3 H + + HCO 3 - Reversible reactions go in the direction of high concentration to low concentration

7.3 Energy Changes in Reactions Heat is a form of energy Chemical energy is energy stored in chemical bonds. Chemical reactions involve the breaking of chemical bonds in the reactants and the formation of chemical bonds in the products.

Energy in Chemical Reactions Activation energy – amount of energy needed to break the bonds of the reactants to start the reaction  Reactants must meet in order to react  When molecules collide, bonds are broken Heat of reaction – energy difference between reactant and products  Exothermic reactions release heat  Endothermic reactions absorb heat

Rate of Reaction Reactions with low activation energy go faster Higher temperature increases reaction rate Amount of reactants affect rate  2 hydrogen molecules in 200 oxygen molecules will only produce 2 water molecules Catalyst – a substance whose presence speeds up a reaction

time energy Energy of reactants Energy of products Exothermic Reaction Energy of Activation Heat Off Heat of Reaction (released)

Endothermic Reaction energy time Heat of Reaction (absorbed) Energy of reactants Energy of products Energy of Activation

Chemical Catalysts Catalyst – speeds up a reaction but does not take part in the reaction and is not used up during the reaction Enzyme – a catalyst in a living organism  Enzymes digest food  Enzymes cause the blood in a wound to clot

CO 2 + H 2 0 H 2 CO 3 H + + HCO 3 -

The End