Chemical Reactions
Chemical formula - tells you how many atoms of each element are in a compound example: CO 2 (carbon dioxide) has one carbon atom and two oxygen atoms 2 points
Chemical Equation - a short, easy way to show a chemical reaction, using symbols The substances you begin with are called the reactants. The new substances formed from the reaction are called the products. = yields 4 points
The subscript (small number to the right of the element s symbol) tells you how many atoms of that element are in the molecule. The coefficient (number to the left of the element s symbol) tells you how many molecules of that compound or element are present. 2 points
Count the Atoms C 6 H 12 O 6 = C atoms = H atoms = O atoms = total atoms
Count the Atoms 3H 2 O = H atoms = O atoms = total atoms
Count the Atoms 5H 2 SO 4 = H atoms = S atoms = O atoms = total atoms
Count the Atoms (NH 4 ) 2 SO 4 = N atoms = H atoms = S atoms = O atoms = total atoms
Conservation of Mass matter is not created or destroyed during a chemical reaction
Balancing Chemical Equations a balanced chemical equation must show the same number of each type of atom on both sides of the equation
When balancing a chemical equation, you can change the coefficient, but you can t change the subscript as that would form a new substance. H 2 O vs. H 2 O 2 Two scientists walk into a bar...
Steps to balancing a chemical equation: For the next 4 slides, make 2 columns on your paper like this: Write the rules on the left side of the page and work the example on the right side of the page.
Steps to balancing a chemical equation: 1. Write the equation. H 2 + O 2 H 2 O
Steps to balancing a chemical equation: 1. Write the equation. 2. Count the atoms of each type of element on both the reactant and product sides of the equation. H 2 + O 2 H 2 O H = 2 H = O = 2 O = 2 1
Steps to balancing a chemical equation: 1. Write the equation. 2. Count the atoms of each type of element on both the reactant and product sides of the equation. 3. Use coefficients to balance the number of atoms on both sides of the reaction. H 2 + O 2 H 2 O H = 2 4 H = 2 O = 2 O = 1 4 2 H 2 2 + O 2 H 2 2 O
Steps to balancing a chemical equation: 1. Write the equation. 2. Count the atoms of each type of element on both the reactant and product sides of the equation. 3. Use coefficients to balance the number of atoms on both sides of the reaction. 4. Look back and check that the equation is balanced. 2H 2 + O 2 2H 2 O
Let s try another one: CH 4 + O 2 CO 2 + H 2 O Count the atoms: C = 1 C = 1 H = 4 H = 2 O = 2 O = 3
Change the coefficients to balance the hydrogen atoms: Now, change the coefficients to balance the oxygen atoms: 2 CH 4 + O 2 2 CO 2 + H 2 O C = 1 C = 1 H = 4 H = 2 O = 2 4 O = 3 4 4 Check to make sure the equation is balanced.
Balance the Equations Mg + O 2 MgO FeS + HCl FeCl 2 + H 2 S 2 points
Physical Change - alters the form or appearance of a substance but does not change it into a new, different substance
Chemical Change (aka chemical reaction) - forms one or more new substances with properties different from those of the original substances
Evidence for Chemical Reactions 1. color change 2. odor
3. formation of a precipitate, a solid that forms when two liquids are mixed* Mercury Acetate and Sodium Iodide form Mercury Iodide Potassium Iodide and Lead Nitrate form Lead Oxide Barium Chloride and Sodium Sulfate form Barium Sulfate
4. production of a gas (seen as bubbles in liquid)*
5. energy changes energy is absorbed in an endothermic reaction energy is released in an exothermic reaction 2 points
Five types of chemical reactions 1. Synthesis - two or more simple substances combine to form a more complex substance A + B AB (two or more reactants; one product) ex: formation of water, 2H 2 + O 2 2H 2 O 2 points
2. Decomposition - a compound breaks down into simpler substances AB A + B (one reactant; two or more products) ex: hydrogen peroxide decomposes to form water and oxygen 2H 2 O 2 2H 2 O + O 2 2 points
3. Single Replacement - one element replaces another in a compound A + BC B + AC C + 2Cu 2 O 4Cu + CO 2 2 points
4. Double Replacement - two elements in different compounds trade places * AB + CD AD + CB FeS + 2HCl FeCl 2 + H 2 S (iron sulfide + hydrochloric acid iron chloride + hydrogen sulfide) 2 points
5. Combustion - oxygen combines with a carbon compound to form water and carbon dioxide C # H # + O 2 CO 2 + H 2 O exothermic 2 points
Activation Energy - the minimum amount of energy needed to get a chemical reaction started
Rates of Chemical Reactions - chemists can speed up or slow down chemical reactions by changing one or more of the following factors: Surface Area - increasing the surface area where a reaction takes place will increase the rate of the reaction Chewing food provides increased surface area; faster digestion 3 points
brain is folded to increase surface area; more chemical reactions can take place simultaneously
grinding a reactant into a powder creates more surface area; increases the rate of a reaction
Temperature - increasing the temperature will increase the rate of the reaction; decreasing the temperature will decrease the rate of the reaction
Concentration - the amount of a substance in a given volume (its strength)
increasing the concentration of the reactants increases the rate of the reaction
Catalyst - a material that increases the rate of a chemical reaction by lowering the activation energy Elephant Toothpaste
an enzyme is a biological catalyst
Inhibitor - decreases the rate of a reaction by preventing reactants from coming together
52 points possible