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Umnica [9.8K]
3 years ago
6

A 50-gram sample has a half-life of 12 days. How much material will remain after 12 days?

Chemistry
2 answers:
Elis [28]3 years ago
8 0
<span>A 50-gram sample with a half-life of 12 days will have a remaining mass of 25 grams after its 12-day half-life. Every cycle of a half-life, the sample will lose half of its mass, so if the half-life, itself, is 12 days and the time period passing is 12 days, one half-life has passed and the material will be halved.</span>
Rom4ik [11]3 years ago
7 0

Answer:25 grams

Explanation:

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12. How many moles of atoms are present in 154 g of Na2O?
tia_tia [17]

Answer:

\boxed {\boxed {\sf A. \ 2.48 \ mol \ Na_2O}}

Explanation:

We are asked to convert an amount in grams to moles. To do this, we use the molar mass. This is the number of grams in one mole of a substance. It is the same value numerically as the atomic mass on the Periodic Table, however the units are grams per mole, not atomic mass units.

Look up the molar masses for the individual elements.

  • Sodium (Na): 22.9897693 g/mol
  • Oxygen (O): 15.999 g/mol

Look back at the formula: Na₂O. Notice there is a subscript of 2 after sodium. This means there are 2 atoms of sodium in every molecule, so we have to multiply sodium's molar mass by 2 before adding oxygen's.

  • Na₂O: 2(22.9897693 g/mol)+ 15.999 g/mol = 61.9785386 g/mol

Set up a ratio using the molar mass.

\frac {61.9785386 \ g \ Na_2O}{1 \ mol \ Na_2O}

Multiply by the given number of grams.

154 \ g \ Na_2O*\frac {61.9785386 \ g \ Na_2O}{1 \ mol \ Na_2O}

Flip the ratio so the grams of sodium oxide can cancel each other out.

154 \ g \ Na_2O*\frac {1  \ mol \ Na_2O}{61.9785386 \ g \ Na_2O}

154 *\frac {1  \ mol \ Na_2O}{61.9785386 }

\frac {154}{61.9785386 }  \ mol \ Na_2O

2.48473106141 \ mol \ Na_2O

The original measurement of grams given has 3 significant figures, so our answer must have the same. For the number we calculated, that is the hundredth place.

  • 2.48<u>4</u>73106141

The 4 in the thousandth place tells us to leave the 8.

2.48 \ mol \ Na_2O

There are <u>2.48 moles of sodium oxide</u> in 154 grams, so choice A is correct.

6 0
3 years ago
Why is there a discrepancy between a heat of reaction ob-tained from calorimetry and one obtained from bond energies?
Eva8 [605]

While bond energies and bond enthalpies can be used to estimate the heat of reaction (enthalpy change of a reaction), H, the heat of neutralization is the heat released when 1 mole of water is generated by the reaction of an acid and a base (reaction).

For the same type of bond, bond enthalpies differ from compound to compound. For instance, the C-H bond enthalpy in methane is nearly identical to that of ethane, butane, etc. When we look up the bond enthalpy for a C-H bond in a table of bond enthalpies, the average number that results may only be accurate to two or three significant figures.

Each compound's enthalpies of production are listed, and those numbers take into account any minor variations in the enthalpies of each bond. Therefore, the result will be more accurate if you utilize formation enthalpies rather than average bond enthalpies to compute a given reaction's enthalpy change.

Learn more about Bond enthalpy here-

brainly.com/question/9998007

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7 0
1 year ago
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vlada-n [284]

Answer:

<h2><u>natural</u></h2>

Explanation:

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8 0
3 years ago
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How many moles of O2 are made from 4 moles of H2O
algol13
Eight moles of O2 are found in 4 moles of H2O
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What are the coefficients for the reaction _Cl2O5 + _H2O → _HClO3 once it is balanced?
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Cl2O5+H20-->2HClO3

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5 0
3 years ago
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