topic: predicting amounts of reagents needed or amounts of products made do now:
DESCRIPTION
TOPIC: Predicting amounts of reagents needed or amounts of products made Do Now:. Coefficients in Chemical Equations. Numbers in front of formulas called coefficients Microscopic: Coefficients represent numbers of individual atoms or molecules Macroscopic: Coefficients give mole ratios! - PowerPoint PPT PresentationTRANSCRIPT
TOPIC: Predicting amounts of reagents needed or
amounts of products made
Do Now:
Coefficients in Chemical Equations• Numbers in front ofin front of formulas called coefficients
– Microscopic: Coefficients represent numbers of individual atoms or molecules
– Macroscopic: Coefficients give mole ratios!– Moles connected to mass
Coefficients in Balanced EquationsMOLE-MOLE word problems: convert from
moles of one substance to moles of another substance
2 C2H6 + 7 O2 4 CO2 + 6 H2O
How much CO2 will be produced if 4 moles of C2H6 are consumed?
1) Start with balanced chemical equation
2) Problem will ask how many moles/liters given will yield certain amount something else
3) Use a proportion to compare old mole/liter amounts to the new mole/liter amounts
2 C2 C22HH66 + 7 O2 4 CO4 CO22 + 6 H2O
How much COCO22 will be produced if 4 moles of CC22HH66 are consumed?
4 moles C2H6= X moles CO2
X = 8 moles CO2
2 C2 C22HH66 + 7 O2 4 CO2 + 6 H6 H22OO
How much HH22OO will be produced in the combustion of 5 moles of CC22HH66?
5 moles C2H6= X moles H2O
X = 15 moles H2O
2 C2 C22HH66 + 7 O7 O22 4 CO2 + 6 H2O
How much oxygenoxygen will react with 5 moles of CC22HH66?
5 moles = X moles
X = 17.5 moles O2
Gas-Phase Equations
• coefficients in equations represent ratio of volumes of gases involved in rxn
• volume-volume word problems: rxns where ALL reactants & products are gases • volume unit (liter/milliliter) doesn’t matter as long as
constant throughout
N2(g) + 3 H2(g) 2 NH3(g)
How much hydrogen gas will react with 15 liters of nitrogen gas?
_________
15 L N2(g)=
X L H2(g)
_________
X = 45 L H2(g)
1
Mass-Volume Problems
• REMINDER: 1 mole any gas occupies same volume as any other gas (At STP = 22.4 L/mol)
• REMINDER: 1 mole = gram formula mass–CO2 = 12 + 16 + 16 = 44 g/mol
What volume of Cl2(g) measured at STP is produced when 7.65g HCl (aq) reacts with
MnO2
MnO2(s) + 4HCl(aq) MnCl2(aq) + Cl2(g) + 2H2O(l)
1. CONVERT TO MOLES
7.65g HCl mol = .2125 mols HCl
36 g HCl
2. Set up ratio 4 = 1 = .053125 mols Cl2
.2125 X
3. Convert Moles to Liters
.053125 mols Cl2 22.4 L = 1.19 L
1 mol
What mass of NH3(g) is produced when 2.15L of H2(g) measured at STP reacts?
3H2(g) + N2(g) 2NH3(g)
1.Set up Ratio 3 = 2 = 1.43 L NH3
2.15 X
2. Convert L to Moles 1.43 L mol = .064 mol NH3
22.4 L
3. Convert Moles to grams .064 mol 17 g = 1.09 g
mol