Chemical Reactions Combining elements

The Law of Conservation of Mass The Law of Conservation of Mass states that the amount of matter in the universe is constant This means that you can’t really ever destroy or create anything, you just change it from one form to another!

Chemical formulas Na + Cl  NaCl Chemical reactions have 2 parts, the reactants and the products Think of the reactants as the “ingredients” of the reaction – what goes in. The products are what comes out. Na + Cl  NaCl Sodium and chlorine are the reactants … and salt is the product. Products Reactants

Numbers and letters The letters are the chemical symbols – N for nitrogen, C for carbon, etc. They always start with a CAPITAL letter. If there is a capital next to another capital, it is two different elements. NaOH is sodium, oxygen and hydrogen KCl is Potassium and chlorine

The little numbers after the symbols are called subscripts, that’s how many of each type of atom is in a compound. NaCl has 1 sodium and 1 chlorine atom H2O has 2 hydrogen atoms and 1 oxygen atom C6H12O6 has 6 carbon, 12 hydrogen, and 6 oxygen atoms

If there are parentheses, you multiply the number outside by the number inside to find the total – Al2(SO4)3 has 3 sulfur and 12 oxygen atoms Coefficient – the large number in front, it means that is the number of molecules. If there is no number, assume it is 1. 6HNO3 means that there are 6 hydrogen, 6 nitrogen, and 18 oxygen atoms in this molecule

Review How many of each type of atom are in: HNO3 C6H18 3CCl4 2MgCl2 Cu(NO3)2

Chemical Formulas and the Law of Conservation of Matter In a formula, the number of atoms stays the same. If you have 20 atoms in the reactants, there must be 20 in the products. Does this equation follow the law of conservation of mass? H2 + O2  H2O No, because there are 2 O atoms on the left and only one on the right. What about now…? 2H2 + O2  2H2O Yes, now there are equal numbers of atoms on both sides

Are these balanced? Al + Cl2  AlCl3 No, there are too many chlorine atoms in the reactants. 2HCl + Na2S  H2S +2NaCl It is already balanced! NaCl + CaSO4 Na2SO4 + CaCl2 No, the chlorine and sodium atoms are not balanced. KOH + HCl  KCl + H2O

Energy Chemical reactions always either release or absorb energy (heat) When they absorb energy, it is known as an endothermic reaction When they release heat it is called an exothermic reaction Photosynthesis (when plants make sugar using carbon dioxide and water) is endothermic – it absorbs energy from the sun. A campfire burning is exothermic – it releases energy from the wood.

Types of Reactions Synthesis – a complex molecule is created from simple molecules 2H2 + O2  2H2O Decomposition – Simple molecules are created from a complex molecule H2CO3 H2O +CO2 Single replacement – An element takes the place of another element Zn + 2HCl  ZnCl2 + H2 Double replacement – ions in different compounds switch places NaCl + AgNO3  NaNO3 + AgCl

Compounds Compound - a pure substance composed of two or more elements chemically combined Molecule – smallest piece of a compound – made of atoms chemically bonded together. Hydrogen Carbon Oxygen Molecule Compound

Types of Compounds Ionic Covalent Acids Bases Salts Organic Compounds

Acids pH < 7 Substance that releases hydrogen ions when dissolved in water Taste sour Conduct electricity Turn blue litmus paper red Turn cabbage juice red HCl – Hydrochloric Acid – in the stomach for digestion H2SO4 – Sulfuric Acid – in batteries

Bases pH > 7 Substance that releases OH- ions in water Taste Bitter Conduct electricity Turn red litmus paper blue Turn cabbage juice blue Feel slippery NaOH – Sodium Hydroxide (lye) - in cleaners NH3 – Ammonia

Salts Substance formed from positive ion of a base and the negative ion of an acid When an acid and a base are combined, they produce a salt and water HCl + NaOH  NaCl + H2O Acid Base Salt Water This is known as neutralization

c Organic Chemistry The Chemistry of Carbon More than 90% of known compounds are organic. Because carbon has 4 valence electrons, each atom can form 4 bonds. Carbon can combine in many ways with itself and other elements to form all living things. c

The Big Six CHNOPS elements found in living things: Carbon Hydrogen Nitrogen Oxygen Phosphorous Sulfur CHNOPS

Biochemicals organic compounds made by living things Carbohydrates There are four types Carbohydrates 1 or more simple sugars bonded together; used as a source of energy Sugars and starches Energy and energy storage Glucose – C6H12O6

2. Lipids 3. Proteins Do not dissolve in water Fats, oils and waxes Store energy, make up cell membranes, moisture for skin 3. Proteins Structure, store materials, transport, regulate chemical reactions Enzymes, antibodies Built of amino acids Lipid! Protein!

4. Nucleic Acids – DNA and RNA Blueprint for life Tell your body what proteins are needed to make… you! ..and every other living thing In the nucleus of every cell of every living thing on Earth.

Polymers Organic compounds in long chains Useful! Low melting point, flexible, easily molded A little variation and they can be made harder, softer, tougher, weaker, etc. Rubber, polyethylene (in plastic bags, etc.), nylon, PVC,