Chemical Reactions Physical Change Chemical Change Chemical Change

Chemical Reactions

Physical Change Chemical Change

Chemical Change • • 1. 2. 3. 4. Reactants Products Signs of a chemical change Color change Production of a gas Formation of a precipitate Energy change • • Exothermic vs. endothermic Occurs as bonds are broken or formed

Chemical Formulas • Shows the number of atoms of each element in a compound – Subscripts below the symbol indicate the number of atoms – Use the distributive property for subscripts outside parentheses • Determine the number of each type of atom in the following compounds 1. H 2 O 2. C 12 H 22 O 11 3. Ca(CO 3)2 4. (NH 4)3 PO 4 5. Pb(Cl. O 3)4 6. Ba 3(As. O 4)2

Chemical Formulas: Covalent Compounds • • Prefixes indicating the number of each atom are used in naming molecules Ex: 1. 2. 3. 4. 5. 6. carbon tetrachloride P 2 O 5 CO dinitrogen trioxide dinitrogen pentoxide S 3 Cl 7 Number of atoms Prefix 1 mono- (not used for first element) 2 3 4 5 6 7 8 9 ditritetrapentahexaheptaoctanona-

Chemical Formulas: Covalent Compounds • 1. 2. 3. 4. • 5. 6. 7. Write the prefix for the number indicated. 9 7 8 6 Write the name or the formula. NO 8. dinitrogen tetroxide Si. O 2 9. sulfur hexafluoride P 3 Cl 5 10. dihydrogen monoxide

Chemical Formulas: Ionic Compounds • To write the formula: 1. Determine the charge on the ions using the PT. – Some charges are written on transition metals 2. Balance the charges to make a neutral compound. 3. Add subscripts to indicate the number of each element. • Examples: – barium fluoride – aluminum oxide Do “Forming Compounds”

Chemical Equations • Reactions are written for chemical changes – Use correct chemical formulas – Reactants Products • Due to the Law of Conservation of Mass, the number of atoms of each element on the reactant side = number of atoms of each element on the product side – Use coefficients to balance equations – Do not change subscripts (they’re determined by neutralizing charges when writing formulas) Use “balancing chemical equations” handout

Reaction Types • Synthesis- makes one product – _____ + _____ – A+B AB – AB + C ABC • Use paper clips! _____ Decomposition- one reactant – _____ – ABC AC + B – AB A+B _____ + _____ (How are synthesis and decomposition related? )

Reaction Types • Single Replacement- one element replaces another that is in a compound – – • Element + compound _______ + ______ AB + C A + CB AB + C AC + B compound + element _____ + _____ Positive ions are always written 1 st ! Double Replacement- 2 compounds switch ions – Compound + compound – _______ + ______ – AB + CD AD + CB compound + compound _____ + _____