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The Math of Equations

The Math of Equations. Stoichiometry the calculation of quantities in chemical reactions. Limiting Reactant. Calculate the amount of product that could be made for each reactant

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The Math of Equations

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  1. The Math of Equations • Stoichiometry the calculation of quantities in chemical reactions

  2. Limiting Reactant • Calculate the amount of product that could be made for each reactant • Compare the amount that could be made to the amount of product actually made to determine which reactant is limiting • Calculate the excess reactant by calculating the amount that actually reacts and then subtracting

  3. Limiting Reactant • There is always some unreacted chemical • Because you cannot measure to the last atom • So one reactant gets used up first • Once one reactant is used up, no more product can be made • The Chemical used up first is the LIMITING REACTANT

  4. Excess reactant • So…….. reactant that is not all used up in the reaction

  5. 2H2 +O2 2H2O • 1. Determine the limiting reactant when.. • 4 grams of H2 are reacted with 31g of O2. • Determine moles of products each reactant can form • The one that is limiting will form the least amount of product 4g H2 x 1 mole H2 x 2 moles H2O = 2 moles H2O 2 g H2 2 moles H2 31g O2 x 1 mole O2 x 2 moles H2O = 1.93 moles H2O 32 g O2 1 moles O2 Oxygen would run out first, that’s why it makes less water. Oxygen is the limiting reactant

  6. Mg + 2HCl  MgCl2 + H2 3.500 g of Mg is added to 300.0 mL of 1.000 M HCl How many grams of Magnesium chloride are formed? 3.500g Mg x 1 mole x 1 mole MgCl2 x 95.21 g MgCl2 = 13.71gMgCl2 24.31 1 mole Mg mole MgCl2 0.3000L x 1.000mole x 1 mole MgCl2 x 95.21 g MgCl2 = 14.28gMgCl2 1 L 2 mole HCl mole MgCl2 Since Mg “runs out first”, it is the limiting reactant. What test could you run to determine there was acid left over?

  7. Mg + 2HCl  MgCl2 + H2 • 3.5 g of Mg is added to 300.0 mL of 1.0M HCl • How many liters of gas @ STP? • Since magnesium is the limiting reactant 3.500g Mg x 1 mole x 1 mole H2 x 22.4 L H2 = 6.450 L H2 24.31 1 mole Mg mole H2

  8. Mg + 2HCl  MgCl2 + H2 • What is left over and how many moles? • If magnesium is the LR, then HCl is left over 3.500g Mg x 1 mole x 2 mole HCl = .2879 moles HCl used in reaction 24.31 1 mole Mg 0.3000L x 1.000mole HCl = .3000 moles HCl given 1 L 0.3000 moles HCl - 0.2879 (moles HCl used by Mg) = .0121 molsHCl 0.0121moles HCl = .0403 M .0121moles HCl x 36.5g = 0.4417g 0.3000L mole HCl

  9. Interpreting Balanced equations 2H2O  2H2 + O2 2molecules 2molecules + 1molecule 2mole 2mole + 1 mole

  10. Steps in stoichiometry • Write symbols and balance • Write the moles on top/known on bottom • Circle the known and unknown • Do Dimensional analysis problem

  11. Mole – Mole problems Ammonium nitrate decomposes to yield dinitrogen monoxide and water How many moles of water are produced if 14.8 moles of ammonium nitrate react? • Write symbols and balance • Write the moles on top/known on bottom • Circle the known and unknown • Do Dimensional analysis problem

  12. practice • Bubbles of hydrogen gas and iron(III) chloride are produced when iron is dropped into hydrochloric acid • How many moles of hydrogen are produced when 14.5 moles of iron react?

  13. Mole – Mass problems Aluminum and silver nitrate react. How many moles of aluminum nitrate will be produced if 34.6 g of aluminum react? • Write symbols and balance • Write the moles on top/known on bottom • Circle the known and unknown • Do dimensional analysis problem

  14. Mass-Mass Lithium nitride reacts with water to produce ammonia and lithium hydroxide. How many g of LiOH are produced if .38g of Li3N react?

  15. Other Sodium chloride is produced when chlorine reacts with sodium 1.How many L of Chlorine are needed to make 45.6 g sodium chloride? 2.How many F.U. of NaCl are produced when 1.32 x 1015 atoms of Na react?

  16. Law of Conservation of Matter Prove the law of conservation of matter for 2NH3 N2 + 3H2 Do Dimensional analysis problem for each reactant and product to determine the mass in g

  17. % Yield (product) % Yield = Actual (experiment) x 100% (product) Theoretical (calculation)

  18. 13.5 g of sodium metal reacts with excess hydrochloric acid. How many liters of hydrogen are produced (at STP… 22.4L / mol) You Try 2Na + 2HCl  2 NaCl + H2 13.5g Na x 1 mol Na x 1 mol H2x 22.4L H2= 23.0 g Na 2 mol Na 1 mol H2 6.57 liters of H2 gas • Steps to solve • Predict products • Balance equation • Set up Dimensional analysis • Solve

  19. 15.0 g of aluminum are reacted with excess oxygen. How much oxide was produced? 4Al + 3O2 2Al2O3 15.0g x 1 mole 27.01 g x 2 mol Al2O3 4 mole Al x 102.g Al2O3 = 1 mol Al2O3 28.3 g aluminum oxide

  20. Matter is Conserved 2H2 + O2 —> 2H2O 4g + 32g = 36g 8g + 64g = ??g 8g + 64g = 72g If you react 8 grams of hydrogen and 64 g of oxygen, how much water would did you make? Four Moles of H2O! Or 4 x 18 g/mole = 72 grams

  21. How many grams of water are produced from 2 moles of hydrogen gas and 1 mole of oxygen gas? 2H2 + O2 —> 2H2O • 2 moles of H2 = how many grams? • 2 mole x 2 atoms x 1 g/mole = 4g • 1 mole of O2 = how many grams? • 2 atom x 16 g/mole = 32 g • 2 mole of H2O = how many grams • 2 mole x 18 g/mole = 36g 4g 32g 36g

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