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aev [14]
3 years ago
13

How many atoms are in a sample of 72.8 grams calcium ?

Chemistry
1 answer:
MArishka [77]3 years ago
6 0
First find the moles
moles of the calcium= 72.8 / 40
moles of calcium in 72.8g = 1.82mol

number of atoms= moles x Avogadro constant
atoms = 1.82 x 6.02x10+23
so the number of atoms is 1.096x10+24
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Problem 4
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<h3>Answer:</h3>

1.93 g

<h3>Explanation:</h3>

<u>We are given;</u>

The chemical equation;

2C₂H₆(g) + 7O₂(g) → 4CO₂(g) + 6H₂O(l) ΔH = -3120 kJ​

We are required to calculate the mass of ethane that would produce 100 kJ of heat.

  • From the equation given;
  • 2 moles of ethane burns to produce 3120 Kilo joules of heat
  • Therefore;

Number of moles that will produce 100 kJ will be;

= (2 × 100 kJ) ÷ 3120 kJ)

= 0.0641 moles

  • But, molar mass of ethane is 30.07 g/mol

Therefore;

Mass of ethane = 0.0641 moles × 30.07 g/mol

                          = 1.927 g

                          = 1.93 g

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We solve first for the amount of carbon dioxide in moles by dividing the given volume by 22.4L which is the volume of 1 mole of gas at STP.
                            moles of CO2 = (5.6 L) / (22.4 L/1 mole)
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Then, we can see that every mole of carbon dioxide will need 1 mole of methane
                              moles methane = (0.25 moles CO2) x (1 moles O2/1 mole CO2)
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