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3 years ago

Which substances have /_\Hf = 0 kJ/mol by definition? Select all that apply.

2 answers:

8 0

Answer: O₂(g), Br₂(l) Fe(s), He(g)


Justification:

1) The state variable given, ΔHf°, is the standard enthalpy of formation. By definition it is the change in the enthalpy that accompanies the formation of a mole of compound in the standard state, from its constituent elements in the standard state.


2) Since the standard state of O₂(g), Br₂(l) Fe(s), He(g) is the very same shown, they do not evolve any heat for its formation. This is, that is the same state of the constituents, and no change is involved.


That is why, ΔHf°, of those elements is 0.

weeeeeb [17]3 years ago

4 0

The answers are O2(g), Br2(I), Fe(s), He (g).

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In the second step of this reaction, isocyanic acid reacts to form melamine and carbon dioxide: HNCO(l)→C3N3(NH2)3(l)+CO2(g) Bal

kykrilka [37]

Answer:

The coefficients are 6, 1, 3

Explanation:

HNCO →C3N3(NH2)3 + CO2

From the above equation, there are a total of 6 atoms of nitrogen on the right side and 1atom on the left. It can be balance by putting 6 in front of HNCO as shown below:

6HNCO → C3N3(NH2)3 + CO2

Now there are 6 atoms of carbon on the left side and 4 atoms on the right side. It can be balance by putting 3 in front of CO2 as shown below:

6HNCO → C3N3(NH2)3 + 3CO2

Now the equation is balanced as the numbers of atoms of the different elements on both sides of the equation are the same.

The coefficients are 6, 1, 3

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3 years ago

Fossil A is estimated to be 5,000 years old and fossil B is estimated to be 2,000 year old. If the two fossils had the same amou

elena-14-01-66 [18.8K]

The new fossil i.e, Fossil B (2,000 year old) contains more carbon-14 than the old fossil i.e, Fossil A (5,000 years old ) does.

<h3>What are Fossils ?</h3>

Fossils are the preserved left materials of ancient organisms in trace form.

Fossils are not just the remains of the organism But also the rocks.

Carbon 14 works to analyse the period organic remains that are between 100 years old (minimum) and about 50,000 years old, (maximum).

If it is new, than not enough time has passed for radioactive decay to produce and if it is older than that, the amount of radioactive decay has dropped so less amount which means that anything beyond 50,000 years old becomes gibberish and may lead to high or low (usually low) concentration.

Hence,the new fossil Fossil B (2,000 year old) contains more carbon-14 than the older Fossil A (5,000 years old ) does.

Learn more about Fossil here ;

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2 years ago

How are dissolved minerals in water related to sedimentary rocks?

emmasim [6.3K]

Because they are both broke apart over time

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3 years ago

The process of an element breaking down over time, allowing geologists to get the absolute age is called _________.

NNADVOKAT [17]

Answer:

radioactive decay

Explanation:

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3 years ago

Draw the two chair conformations of cis 1 chloro 2 methylcyclohexane

Mrrafil [7]

In chair conformations of cyclohexane, Cl group is on the first C and methyl group is on the second C. In the cis conformation both groups should be in the same orientation, either both side chains should be up and up or down and down. In this figure its up and up.
2 figures are drawn as when the chair conformation flips, the axial groups become equatorial and equatorial groups become axial. But they remain as up or down .
When A flips to B, Cl goes from axial to equatorial and CH3 goes from equatorial to axial but both remain up.

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4 years ago