Unit 4: Stoichiometry of Chemical Reactions
How a balanced equation becomes a recipe you can scale, and what actually happens, ion by ion, when two solutions meet.
12 topics · 46 questions
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4.1 Balancing Chemical Equations
- Common mistakeWhy can't you balance an equation by changing the subscripts inside a chemical formula?
- How it worksHow do you use trial and error with coefficients to balance the combustion of propane, C3H8?
- Worked exampleFind the balanced equation for the reaction between aluminum metal and oxygen gas forming aluminum oxide.
Your turn1 of 2
Why does a chemical equation have to show the same number of each type of atom on both sides before it counts as balanced?4.2 Reaction Types: Combination, Decomposition, and Displacement
- How it worksHow do you tell a single replacement reaction apart from a double replacement reaction just from the reactants?
- How it worksWalk me through predicting the products when magnesium metal is dropped into hydrochloric acid.
- Worked exampleFind the products formed when solid calcium carbonate decomposes on heating.
- Going furtherWhat happens to a single replacement reaction's outcome when the metal being added is less reactive than the one already in solution?
Your turn1 of 2
How do you tell a single replacement reaction apart from a double replacement reaction just by looking at the reactants?4.2 Combustion Reactions of Hydrocarbons
- How it worksHow do you balance a combustion equation by handling carbon, then hydrogen, then oxygen last?
- Worked exampleFind the balanced equation for the complete combustion of butane, C4H10.
- Going furtherWhat happens to the products of combustion when there isn't enough oxygen available to react completely?
Your turn1 of 2
A hydrocarbon has the general alkane formula CnH(2n+2) with n = 7. How many moles of CO2 form when 3.42 mol of it combusts completely?4.3 Mole-to-Mole Stoichiometry from a Balanced Equation
- How it worksHow does a mole ratio taken straight from the coefficients convert moles of one substance into moles of another?
- Worked exampleFind how many moles of water form when 3.00 mol of hydrogen gas reacts completely with oxygen.
- Common mistakeWhy isn't the mole ratio between two substances in an equation the same as the ratio of their masses?
- Ties togetherHow does the mole ratio from a balanced equation connect back to the law of definite proportions?
Your turn1 of 2
Given the balanced equation N2 + 3 H2 → 2 NH3, find how many moles of NH3 form when 10.9 mol of H2 reacts completely with excess nitrogen.4.3 Mass-to-Mass Stoichiometry
- How it worksWalk me through the full grams-to-moles-to-moles-to-grams path that mass-to-mass stoichiometry always follows.
- Worked exampleFind the mass of carbon dioxide produced when 25.0 g of propane, C3H8, burns completely.
- Worked exampleFind the mass of iron produced when 150. g of iron(III) oxide reacts completely with excess carbon monoxide.
- Common mistakeWhy can't you skip straight from grams of reactant to grams of product without ever finding moles along the way?
Your turn1 of 2
In the reaction C3H8 + 5 O2 → 3 CO2 + 4 H2O, find the mass of carbon dioxide (molar mass 44.01 g/mol) produced when 71 g of propane, C3H8 (molar mass 44.10 g/mol), burns completely.4.3 The Limiting Reactant
- How it worksHow do you figure out which of two reactants runs out first in a stoichiometry problem?
- Worked exampleFind the limiting reactant when 5.00 g of hydrogen reacts with 20.0 g of oxygen to form water.
- Worked exampleFind the mass of water produced from the limiting reactant in that same 5.00 g hydrogen and 20.0 g oxygen mixture.
- Common mistakeWhy isn't the reactant with the smaller starting mass automatically the limiting reactant?
- Going furtherWhat happens to the amount of product formed if you double the excess reactant but not the limiting one?
Your turn1 of 2
In the reaction 2 H2 + O2 → 2 H2O, 3 g of hydrogen gas (molar mass 2.016 g/mol) reacts with 66 g of oxygen gas (molar mass 32.00 g/mol). Find the mass of water (molar mass 18.02 g/mol) produced, given that hydrogen is the limiting reactant across this whole range.4.3 Theoretical, Actual, and Percent Yield
- Common mistakeWhy can percent yield land under 100 percent even when every gram of limiting reactant fully reacted?
- How it worksHow does dividing actual yield by theoretical yield and multiplying by 100 turn two masses into one percentage?
- Worked exampleFind the percent yield when a reaction predicted to make 45.0 g of product actually produces only 38.2 g.
Your turn1 of 2
A reaction has a theoretical yield of 88 g but an actual yield of only 39 g. Find the percent yield.4.1 Electrolytes and Solution Conductivity
- How it worksHow do freely moving ions in solution carry electric current the way free electrons do in a wire?
- How it worksWalk me through classifying HCl, NaCl, and glucose dissolved in water as strong, weak, or nonelectrolytes.
- Common mistakeWhy isn't dissolving in water by itself enough to make a substance an electrolyte?
- Going furtherWhat happens to a solution's conductivity when a strong electrolyte is swapped for a weak one at the same concentration?
Your turn1 of 2
Both table salt and sugar dissolve completely in water, yet the salt solution conducts electricity and the sugar solution does not. What explains the difference?4.2 Precipitation Reactions and Net Ionic Equations
- How it worksHow do solubility rules predict whether mixing two ionic solutions will form a solid precipitate?
- How it worksWalk me through stripping the spectator ions out of a full ionic equation to leave only the net ionic equation.
- Worked exampleFind the net ionic equation for the reaction between solutions of silver nitrate and sodium chloride.
- Common mistakeWhy aren't spectator ions written into a net ionic equation even though they're physically present in the beaker?
Your turn1 of 2
How do solubility rules let you predict, before mixing anything, whether combining two ionic solutions will form a precipitate?4.2 Acid-Base Neutralization Reactions
- How it worksHow does a proton transferring from the acid to the base's hydroxide explain water forming every single time?
- Worked exampleFind the balanced neutralization equation between hydrochloric acid and calcium hydroxide.
- Common mistakeWhy isn't the salt produced by a neutralization reaction automatically neutral itself?
Your turn1 of 2
Neutralizing hydrochloric acid with sodium hydroxide, and separately neutralizing nitric acid with potassium hydroxide, both produce water as a product. Why does water form in essentially every acid-base neutralization?4.4 Oxidation Numbers and Oxidation-Reduction Reactions
- How it worksHow do you assign an oxidation number to each atom in a compound like potassium dichromate?
- How it worksWalk me through identifying which element is oxidized and which is reduced when zinc reacts with copper sulfate.
- Worked exampleFind the oxidation number of chromium in the dichromate ion, Cr2O7 2-.
- Common mistakeWhy isn't oxidation only about a substance combining directly with oxygen?
- Ties togetherHow does an oxidation-reduction reaction connect to the electron transfer that runs a galvanic cell?
Your turn1 of 2
In the polyatomic ion X2O74- (overall charge -4), oxygen is -2 in each of its 7 atoms. Find the oxidation number of X.4.5 Titration Stoichiometry
- How it worksHow does the moment an indicator changes color mark the point where moles of acid and base exactly match?
- Worked exampleFind the molarity of an HCl solution if 27.4 mL of it is neutralized by 32.0 mL of 0.150 M NaOH.
- Common mistakeWhy isn't the equivalence point of a titration the same thing as the moment the indicator changes color?
- Going furtherWhat happens to the volume of titrant needed when the unknown acid is diprotic instead of monoprotic?
Your turn1 of 2
Find the molarity of an HCl solution if 38 mL of it is exactly neutralized by 36 mL of 0.47 M NaOH (a 1 to 1 mole ratio).