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Chemical Reactions A chemical reaction is also known as a chemical ______________________________. A chemical reaction is when one or more ____________________________ are changed. Bonds are _______________________________ and rearranged to reform new substances. Reactants Products _________________________ _________________________ There are 6 indicators (observations) of a chemical reaction : _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ In a chemical reaction, the law of _____________________________________ of mass is important. This law states that __________________________ can neither be created nor destroyed, just changed in form. A ___________________________________________ describes a chemical reaction using symbols and formulas. Fe(s) + O2(g) Symbols you should know: (s) _________________________ (g) _________________________ _________________________ _________________________ Fe2O3(s) (l) unbalanced _____________________________ (aq) _____________________________ + _____________________________ X ______________________________ ______________________________ On the product side ONLY __________________________ A chemical reaction must have 2attributes: 1. It must contain correct chemical formulas o BrINClHOF is the mnemonic for all of the 7 diatomic molecules. They get a subscript of 2 when by themselves. o Always check the charges of an ionic compound when translating an equation or predicting a product. 2. It must be balanced! o _the number of atoms of each element on the reactant side must __________________________ the number of atoms of each element on the product side. o ______________________________________are small whole numbers placed in front of a chemical formula in order to balance the atoms o A “1” is understood o The coefficient multiplies by every subscript within a chemical formula Examples: CaCl2 3 CaCl2 3 Ca3(PO4)2 Translating a word equation into a skeletal equation 1. Hydrogen gas reacts with liquid bromine to form hydrogen bromide gas. 2. Carbon monoxide reacts with oxygen gas to form carbon dioxide. 3. Calcium carbonate decomposes to form calcium oxide and oxygen gas Tips for Balancing Equations: 1. Balance each atom one at a time leaving HYDROGEN and OXYGEN for last 2. Balance polyatomic ions that are found on both sides as chunks, instead of single atoms 3. If there is an odd number of an element on one side and an even number on the other side, use a coefficient of 2 to even out the odd number. 4. Combustion reactions are more easily balanced if you start off by balancing the carbon and then hydrogen in the hydrocarbon. Then balance the oxygen last. 5. Once you think the equation is balanced, always recheck and count all atoms over again to make sure they are equal on both sides. 6. If the coefficients can be simplified, do so! Balancing Practice: 1. ___ H2 + ___ Cl2 __ HCl 2. ___ KClO3 ___ KCl + ___O2 3. ___ NH4NO3 + ____ Ca3(PO4) 2 ____ (NH4)3PO4 + ___ Ca(NO3) 2 4. ____ C6H14 + ___ O2 ___ CO2 + ___ H2O 5. _____ Z n + _____ HCl ____ ZnCl2 + ___ H2 5 Types of Reactions 1. Combination (Synthesis): when 2 or more _______________________________ combine to form one single _____________________________. A + B AB 2 or more elements OR 2 or more compounds 1 single product Examples: Fe + S FeS CaO + H2O Ca(OH) 2 2. Decomposition: when 1 _______________________________ breaks down or decomposes to form 2 or more _____________________________________. These require _____________________ to get started such as heat, light, or electricity. AB A 1 single reactant Hg + NaHCO3 O2 Na2CO3 + H2O + B 2 or more elements OR 2 or more compounds Examples: HgO + CO2 3. Single Replacement: when a more reactive element __________________________ a less reactive element. Must use the _______________________________ chart, which predicts if the reaction will take place. Look at your reference sheet for the chart. Elements on the top of the chart are _____________________ reactive than the elements on the bottom. Elements can replace other elements below them on the chart. For example: Lithium can replace Aluminum A + BC AC element & aqueous compound + B element & aqueous compound Examples: Cu + AgNO3 Cl2 + KBr CuNO3 + Ag KCl + Br2 4. Double Replacement: when the positive ions of each aqueous compound replace each other. AB + CD AD 2 aqueous compounds + CB 2 aqueous compounds Examples: KI + Pb(NO3) 2 AgNO3 + KNO3 + CuCl2 PbI2 AgCl + Cu(NO3)2 5. Combustion: the burning of a substance by reacting it with oxygen (O2) Hydrocarbon + O2 Fe Fe2O3 + O2 Examples: CH4 + O2 C4H10 + O2 CO2 + CO2 + H2O H2O CO2 + H2O