Stoichiometry PDF - Past Paper

2021-06-04 Stoichiometry From the Greek stoicheion (“element”) + metron (“measure”)...

2021-06-04 Stoichiometry From the Greek stoicheion (“element”) + metron (“measure”) The mathematical process of calculating the amounts of products Stoichiometry and reactants in a chemical reaction based on the law of conservation of mass The coefficients of a balanced chemical equation provide the ratio between the different compounds involved in a reaction What did you have for lunch? Salad: Coefficients in front of elements and 1 head of lettuce compounds = # of atoms and molecules that 2 tomatoes 1 cucumber participate in a reaction 5 radishes How many tomatoes do I need to make 2 N2(g) + 3H2(g)  2NH3(g) salads? 1 molecule 3 molecules 2 molecules How many salads can I make with: 3 heads of lettuce 6 tomatoes The relative ratios of the coefficients for a 3 cucumbers 15 radishes chemical reaction are CONSTANT The Stoichiometric Ratio Sample Problems A ratio describes a strict mathematical relationship between two N2(g) + 3H2(g)  2NH3(g) values It represents a PROPORTION: A proportion is a general rule; it can be applied to specific values 1. How many molecules of hydrogen are needed to produce 20 molecules of 1 7 For example a ratio of 1:2 or can be related to. In this case, x = 14 2 𝑥 ammonia? 1 𝑥 The same ratio can be also be related to (x = 2) 2 4. By making an equation of the ratios, we can solve for the unknown quantity The general stoichiometric (coefficient) ratio between two 2. How many molecules of hydrogen will react reactants/products in a balanced chemical equation can be applied to with 4.0 × 1025 molecules of nitrogen? specific cases in the same way 3. If you have 36 molecules of ammonia, how much nitrogen do you need? 1  2021-06-04 N2(g) + 3H2(g)  2NH3(g) From Molecule Ratio to Mole Ratio How many molecules of hydrogen are needed to produce 20 molecules of ammonia? In a balanced equation, the coefficients also 3 𝐻2 = 𝑥 𝑥 = 30 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 𝐻2 indicate the mole ratios of reactants consumed 2 𝑁𝐻3 20 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 𝑁𝐻3 and products formed How many molecules of hydrogen will react with 4.0 × 1025 molecules of nitrogen? N2(g) + 3H2(g)  2NH3(g) 3 𝐻2 = 𝑥 𝑥 = 1.2 × 1026 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 𝑜𝑓 𝐻2 1(6.02 × 1023) 3(6.02 × 1023 ) 2(6.02 × 1023 ) 1 𝑁2 4.0×1025 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 𝑁2 molecules molecules molecules If you have 36 molecules of ammonia, how much nitrogen do you need? 1 𝑁2 𝑥 1 mol 3 mol 2 mol = 𝑥 = 18 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 𝑁2 2 𝑁𝐻3 36 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 𝑁𝐻3 Moles accommodate decimals, molecules cannot Sample Problems N2(g) + 3H2(g)  2NH3(g) N2(g) + 3H2(g)  2NH3(g) If you have 3.2 mol of hydrogen, how many moles of ammonia will be produced? 1. If you have 3.2 mol of hydrogen, how many 2 𝑁𝐻3 = 𝑥 𝑥 = 2.13 𝑚𝑜𝑙 𝑁𝐻3 moles of ammonia will be produced? 3 𝐻2 3.2 𝑚𝑜𝑙 𝐻2 In order to produce 4.20 mol of ammonia, how many 2. In order to produce 4.20 mol of ammonia, moles of nitrogen would be required? how many moles of nitrogen would be required? 1 𝑁2 = 𝑥 𝑥 = 2.10 𝑚𝑜𝑙 𝑁2 2 𝑁𝐻3 4.20 𝑚𝑜𝑙 𝑁𝐻3 Different ratios of Reactants Homework Relative amounts of reactants are important Different mole ratios of the same reactants can Read 7.1 produce different products Try the practice problems on pg 319 Complete pg 320 #1,3,4,6-9 2C (s) + O2 (g)  2CO (g) C (s) + O2 (g)  CO2 (g) If there is a relative shortage of oxygen, and the ratio of C:O is closer to 2:1, CO is more likely to be produced instead of CO2 i.e. Complete vs Incomplete Combustion 2