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MED 102- GENERAL CHEMISTRY > 14. CHEMICAL EQUATIONS > Flashcards

14. CHEMICAL EQUATIONS Flashcards

1
Q
  1. What is a chemical equation?
A
  • it is a shorthand way of representing a chemical change
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2
Q
  1. What must the chemical equation obey?
A
  • it must obey the Law of Conservation of Mass
    (mass is neither created nor destroyed)
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3
Q
  1. Must the atoms be balanced in a chemical equation?
A
  • yes
  • there has to be the same number of atoms of each element on the left and the right side
  • you must also include the physical states
    (s, l, g, aq)
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4
Q
  1. Give the name for the following symbols:

4.1: (g)
4.2: (l)
4.3: (s)
4.4: (aq)

A

4.1: substance is a gas

4.2: substance is a liquid

4.3: substance is a solid

4.4: substance exists in aqueous (water) solution

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5
Q
  1. What are the two necessary steps to balance out a chemical equation?
A
  • you must introduce coefficients to balance the number of atoms of each element
  • subscripts must never change
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6
Q
  1. How do we measure mass in the laboratory?
A
  • we measure the mass of the reactants
  • we measure it in grams
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7
Q
  1. With regards to chemical reactions, we need to relate the mass of the reacting atoms and molecules to the number of particles.
    How do we do this?
A
  • We use the following unit:
    • 1 mole = Avogadro’s number
      = 6.022 x 10²³
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8
Q
  1. What is the molar mass?
A
  • it is the sum of all the atomic masses of all the atoms
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9
Q
  1. How is Molar Mass worked out?
A
  • you times the number of the atoms by their atomic mass number
  • always round to two decimal figures
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10
Q
  1. Which equation do we use to calculate the number of moles in a gas, pure liquid or pure solid?
A

n = m/MM

  • n= moles
  • m = mass (grams)
  • MM= molar mass (g/mols)
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11
Q
  1. What is an aqueous solution?
A
  • it is a solute + solvent
  • solute= substance being dissolved
  • solvent= substance doing the dissolving
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12
Q
  1. What does solution concentration depend on?
A
  • the amount of solute
  • the amount of solvent
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13
Q
  1. What is Molarity?
A
  • M= moles of the solute / litres of the solution
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14
Q
  1. What is another way of writing the molarity equation?
A
  • M = n / v
  • M= Molarity (mol/L)
  • n = moles
  • V= volume (in litres)
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15
Q
  1. When do we use the n= M x V equation?
A
  • when we are dealing with aqueous (water) solutions
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16
Q
  1. What are Yields?
A
  • they are a measure of how much product has been lost
  • this is usually compared to the calculated product amount
17
Q
  1. What is the formula for working out the percentage Yield?
A
  • Percentage Yield = Actual yield of the product
    ——————————————- x 100
    Theoretical yield of the product
18
Q
  1. What is the Theoretical Yield of the product?
A
  • it is the amount of product expected to form
  • this is on the basis of stoichiometric calculations
  • it is what we calculate from balanced equations
19
Q
  1. What is the Actual Yield?
A
  • it is the amount of product that was actually formed in the experiment
20
Q
  1. What is the Percentage Yield?
A
  • it is usually less than 100%
  • this is because we get losses in the lab
  • there can also be side products formed
  • it may also appear to be higher than 100%
  • this happens when we have impurities in our product
21
Q
  1. In the equation:
    C3H8 + 5 O2 —-> 3 CO2 + 4 H2O

Which is the excess reactant and why?

A
  • oxygen
  • it is readily available in the air
  • we can use as much of it as we need
22
Q
  1. In the equation:
    C3H8 + 5 O2 —-> 3 CO2 + 4 H2O

Which is the limiting reactant and why?

A
  • propane (C3H8)
  • it is the substance that runs out first
23
Q
  1. What is the amount of product dependent on?
A
  • it depends on the amount of limiting reactant
  • this is because the reaction stops when the limiting reactant is used up
24
Q
  1. How do you work out which one is the limiting reactant?
A
  • you find the number of moles for the atom/molecule
  • you divide this number by the coefficient
  • the smallest number indicates the limiting reactant
25
Q
  1. Does adding more solvent change the number of moles of a solution?
A
  • no
26
Q
  1. How is a solution diluted?
A
  • we start off by taking a small amount of a concentrated solution
  • this concentrated solution is placed in another container
  • water is added to it
  • this dilutes it
27
Q
  1. Does water have an affect on the number of moles?
A
  • no
  • the number of moles of the concentrated solution do not change
  • the number of moles in an aqueous solution is given by the equation: n=M x V
28
Q
  1. What formula do we use to work out the dilution of a solution?
A
  • M1 x V1 = M2 x V2
  • the number 1 indicates the concentrated solution
  • the number 2 indicates the diluted solution
29
Q
  1. Read through this summary.
    Does everything make sense?
A
  • yes
30
Q
  1. Read through this summary.
    Does everything make sense?
A
  • yes

MED 102- GENERAL CHEMISTRY (27 decks)

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