1. Unit 3 Stoichiometry Part 2

2. Mass Relations in Reactions: Reactants – the starting substances in a chemical reaction; found on the left-side Products – the ending substances in a chemical reaction; found on the right-side Yield – the arrow written to separate the reactants and products

3. Mass Relations in Reactions: Subscripts – indicate the number of atoms of each element or ion in a chemical formula Coefficients – the numbers written in front of substances in a chemical equation to indicate the number of “particles” or moles of that substance

4. States of matter Symbols indicating state or condition of a substance in the reaction Aqueous – (aq) a substance dissolved in water Precipitate – (ppt. or ) a solid substance formed from the reaction of aqueous substances Solid – (s) Liquid – (l) Gas – (g)

5. Types of equations 1.Synthesis or combination – when 2 or more reactants react to form 1 product

6. Types of equations 2. Decomposition – when 1 reactant reacts to form 2 or more products

7. Types of equations 3. Single replacement or single displacement – when one element and one compound react and the element replaces one of the ions in the compound to form a new compound and different single element

8. Types of equations 4. Double replacement or double displacement – when 2 compounds react and switch ions to form 2 new compounds

9. Types of equations 5. Combustion – “burning”; when a hydrocarbon reacts with oxygen to form carbon dioxide and water

10. Mole ratios or stoichiometric factors: Equations are balanced in order to obey the Law of Conservation of Mass. As a result, there are mathematical relationships between the substances in a balanced chemical equation which are the foundation of stoichiometry.

11. Example: CS 2 + 3 O 2  CO 2 + 2 SO 2

12. c. For an equation to be balanced… a. sum all atoms of each type on a side, even if an element is in more than one substance b. work from left to right to stay organized c. if a polyatomic ion is present in the same form on both sides it can be counted as a unit rather than as individual elements d. look to balance H’s and O’s last in more difficult equations e. combustion reactions should always be balanced in the order of carbon, hydrogen, oxygens on the right and then the left – and use the doubling rule when you have an odd number of oxygens

13. CS 2 + 3 O 2  CO 2 + 2 SO 2 2. In balanced equations coefficients are then the stoichiometric factors or mole ratios for the substances in that specific reaction. They can be used to relate substance to substance mathematically like any other conversion factor.

14. Example 3.8

15. Predicting Products Synthesis – Put the 2 elements together, positive ion first, and criss cross – balance the overall equation Decomposition – Take the 2 elements apart and check for diatomic elements – balance the overall equation

16. Predicting Products Single replacement – determine the charge on the lone element, replace the same sign charge with it, criss cross, check for diatomic property on the new lone element - balance the overall equation Double replacement – separate the ions, switch the ion’s partners, criss cross – balance the overall equation

17. Predicting Products Combustion – the products are always CO 2 and H 2 O – balance the overall equation using the odd = double rule

18. Stoichiometry Calculating relationships between substances in a balanced equation using mole/mole ratios Stoich map

19. Limiting and Excess Reactants Limiting reactant – the reactant that will be completely used up by the reaction Excess reactant – the reactant that will not be used up by the reaction; there will be some left over when the reaction stops

20. Steps for solving problems: Find the starting amounts of reactants Set up posts for each starting amount Convert each starting amount to the product asked about in the correct unit The final answer is the smaller of the amounts calculated in step 3 The limiting reagent is the original reactant the produced the smaller answer The excess reagent is the original reactant that produced the larger answer

21. Percent Yield: Percent yield – the percentage of the substance actually produced based on the amount that should be produced according to the stoichiometry Theoretical mass of substance – mass determined from the original reactant amounts and stoichiometric calculations Mass of substance actually produced by the reaction x 100 = % yield Theoretical mass of substance produced by the reaction