Chapter III Flashcards
define stoichiometry
relationship between relative quantities of subst. in a chemical equation, a ratio of whole-integer moles
formula for combustion reaction
CₓHᵧ + O₂ (g) → CO₂ (g) + H₂O (l)
s.f. in avogadro’s #
4
How to present “% comp of H mass in H₂O” work (5 steps)
1) OG eqn: % comp H = (g H₂)/(g H₂O) x 100
2) Solved eqn: NA here
3) Subbed units: % comp H = 2(1.008)/(2(1.008) + 15.999)
4) Calc: .11189 x 100
5) S.F.: 11.19% H
what do you need to remember when making empirical formulas?
check if it’s covalent - if it is, then DON’T turn it into an empirical formula bc it’s referencing actual molecule ratios
How to present “what is empirical form of…” work (5 steps)
1) Multiply %comp of element given by 1mol/xg weight of that element on the PT, your answer should be in mol
2) Divide each mol result by the smallest result there to get “parts”
3) write the ratio El₁ : El₂ : El₃ and set it equal to Parts₁ : Parts₂ : Parts₃
4) Multiply the ratio by whatever number it takes to get each one to a whole #
5) Put the empirical formula together
***probably won’t be tested on this but how should you treat an empirical comp w/ Hg2^2+ in it?
don’t reduce it down if it’s divisible by 2
how to show work when finding mol mass of comp, 4 steps
1) OG eqn: mol mass of El₁ + mol mass of El₂
2) Sub in: #g/mol₁ + #g/mol₂
3) Calc answer: XXX.XXX…. g/mol
4) Final answer: XXX.X g/mol
What did you miss in showing your work in those stoichiometry questions you missed?
you have to turn the g of the El₁ into moles, turn that into moles of El₂ thru stoichio, and turn that into g of El₂
How to find limiting reactant
multiply El₁ by the mol:mol ratio between it & El₂ to convert it to mol El₂
If that amt is greater than the amt of El₂ provided, then El₂ is the limiting reactant
define limiting reactant
The limiting reactant is the reactant whose amount is used up earliest in the reaction, thereby “limiting” how much of the product can be made, regardless of the amount of excess reactants.
