Chemical Reactions Fireworks are a result of chemical reactions

Chemical Reactions Chemical Reactions form new substances by breaking and making chemical bonds Chemical reactions change the way the atoms are arranged

Difference between Physical and Chemical Changes A change in the state Solid to liquid Liquid to gas Gas to liquid Atoms/molecules of the substances do not change Chemical Atoms/molecules broken down or combined to form new substances Properties of new substances are different than properties of the substances that make them up

Reactants and Products Reactants: present at the beginning of the reaction Products: are the substances formed by the chemical reaction Example burning natural gas CH4 + 2O2 > CO2 +2H2O Reactants > Products

Evidence of Chemical Reactions Color Change Formation of Precipitate (solid formed from two liquids) Formation of gas Temperature change: endothermic (temp down) exothermic (temp up) Change in smell www.learner.org

Classification of Chemical Reactions Synthesis: a new compound is formed by the combination of simpler reactants Smog formed when nitrogen and oxygen combine N2 +2O2 > 2 NO2 oceanworld.tamu.edu

Classification of Chemical Reactions Decomposition: A reactant breaks down into simpler products (reverse of synthesis) Water can be decomposed into hydrogen and oxygen 2 H2O > 2H2 +O2 www.blewbury.co.uk

Classification of Chemical Reactions Combustion: One reactant is always oxygen and another reactant often contains carbon and hydrogen Burning of methane CH4 + 2O2 > CO2 +2H2O earthguide.ucsd.edu

The Rates of Chemical Reactions can vary Concentration: measures the number of particles present in a certain volume. A high concentration of reactants means there is a large number of particles that can collide and react Turning the valve on a gas stove increases the methane molecules that can combine with oxygen and results in a bigger flame and faster combustion reaction

The Rates of Chemical Reactions can vary Surface Area: the exposed surface of a substance. To increase reaction break a large piece of the material so that there is more surface area of the material Increase surface area=Increase reaction rate

Temperature Rate of reaction can be increased by an increase in temperature which increases how fast the particles are moving and increases the number of collisions Remember the cold and hot water distribution of food coloring

Catalyst Catalyst: is a substance that increases the rate of chemical reaction but is not consumed in the reaction Enzymes are catalysts that are used by living things to cause a chemical reaction. Resulting in a new product being made and the catalyst not being changed.

The masses of reactants and products are equal Law of conservation of mass: states that in a chemical reaction atoms are neither created nor destroyed. (Antoine Lavoisier) All atoms present in the reactants are also present in the products www.iuav.it

Chemical Equations Reactants > Products Balancing Chemical Equations Use conservation of mass to balance: atoms can not be created or destroyed. Reactants = products mooni.fccj.org

Chemical equations CH4 + O2 > CO2 + H2O Balanced? No Reactants: C=1, H=4, O=2 Products: C=1, H=2, O=3 H and O not equal Use coefficients to balance equations CH4 + 2O2 > CO2 + 2H2O C=1, H=4, O=4 > C=1, H= 4, O=4 Equation is now balanced!

Chemical Reactions Involve Energy Changes It takes energy to break chemical bonds. This energy is called bond energy. students.ed.uiuc.edu

Exothermic Reactions Exothermic reaction: energy is released and temp goes up…more energy is released when products are formed. Space shuttle on take off: white clouds of water vapor are formed www.sanchezcircuit.com

Exothermic Reactions Exothermic reactions release energy! www.learner.org Exothermic reactions release energy! All common combustion reactions are exothermic Fireflies release energy in the form of light as an exothermic reaction

Endothermic reactions Endothermic reactions: produce a decrease in temperature because the bond energies of the reactants are greater than the bond energies of the products All endothermic reactions absorb energy! Alka Seltzer and water…temperature goes down.

Endothermic Reactions Photosynthesis (general formula) 6CO2 +6H2O > C6H12O6 +6O2 plants absorb energy from sunlight to turn carbon dioxide and water into oxygen and glucose (sugar). Energy is stored in the glucose molecule to be used when needed. www.osovo.com

Life and Industry depend on Chemical Reactions Living things require chemical reactions Respiration: living things get energy from glucose by respiration. (combustion of glucose) Photosynthesis 6CO2 +6H2O + energy> C6H12O6 +6O2 Respiration C6H12O6 +6O2 > 6CO2 +6H2O + energy Respiration is the opposite of photosynthesis!