Calculate both the number of moles in a sample of chromium containing 5.00 1020 atoms and the mass of the sample.

5.00 atoms containing 8.3 *10^-24 moles this is 4.3 * 10^-22 grams

1020 atoms containing 1.69*10^-21 moles this is 8.8 *10^-20 grams

Explanation:

Step 1: Data given

Sample 1: contains 5.00 chromium atoms

Number of Avogadro = 6.022 * 10^23 / mol

Molar mass of chromium = 52 g/mol

Step 2: Calculate number of moles in 5.00 chromium atoms

Moles = atoms / number of Avogadro

Moles = 5.00 / 6.022 *10^23

Moles = 8.3 *10^-24 moles

Step 3: Calculate mass of 5.00 moles chromium atoms

Mass = moles *molar mass

Mass = 8.3 *10^-24 moles * 52 g/mol

Mass =4.3 * 10^-22 grams

Step 1: Data given

Sample 1: contains 1020 chromium atoms

Number of Avogadro = 6.022 * 10^23 / mol

Step 2: Calculate number of moles in 1020 chromium atoms

Moles = atoms / number of Avogadro

Moles = 1020 / 6.022 *10^23

Moles = 1.69*10^-21 moles

Step 3: Calculate mass of 1020 moles chromium atoms

Mass = moles *molar mass

Mass = 1.69*10^-21 moles * 52 g/mol

Mass = 8.8 *10^-20 grams

"standard molar enthalpy:

h2o ( liquid water ) : - 285.8 kj/mole

h2o ( water vapor ) : - 241.8 kj / mole.

δhrxn = - 241. 8 - ( - 285.8 )= -241.8 + 285.8 = 44.0

answer: 44.0 kj"

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