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earnstyle [38]
3 years ago
5

Why are chemical changes considered “unseen”?

Chemistry
2 answers:
atroni [7]3 years ago
6 0
<span>The correct answer here is that the reason chemical changes can be considered unseen, is because the alterations made within an element when it undergoes a chemical change occurs within the very atoms of the cell itself. In contrast with this, a physical change (such as a solid changing to a liquid through melting) does not change the element itself, but just it's physical form, so this can be seen easily to the human eye.</span>
enot [183]3 years ago
5 0

Answer is: chemical changes are considered "unseen", because they occur at the atomic level.

There are two types of substance changes: chemical and physical.

In chemical change (chemical reaction) new substances are formed, the atoms are rearranged (atoms are invisible to human eyes).

Physical property can be observed and measured without any changes in molecular composition. The same substance is present before and after the psysical change, just with different form or state of matter, this changes are seen by human eyes because of change of color or state of matter.

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The atomic particles given off as a result of nuclear fusion are?
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Answer:

I think <em><u>alpha</u></em> and <em><u>beta</u></em> is the answer.

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How does the law of conservation of mass apply to this reaction C2H4+4O2--&gt;4H2O+2CO2 .Only the oxygen needs to be balanced B.
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C2H4+4O2-->4H2O+2CO2

the answer is C
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sp2 hybrid orbitals have 1. trigonal bipyramidal symmetry. 2. linear symmetry. 3. tetrahedral symmetry. 4. trigonal planar symme
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Answer:

4. trigonal planar symmetry.

Explanation:

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Hence, the correct answer is "4. trigonal planar symmetry.".

7 0
3 years ago
Explain why the Chemicals properties of Mg 24 12 and Mg 26 12 are the same
Volgvan

Answer:

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Explanation:

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3 years ago
Promethium-147 is sometimes used in luminescent paint. It has a half-life of 956.3 days. If 250 grams (g) of promethium-147 is u
Fantom [35]

Answer:

% = 76.75%

Explanation:

To solve this problem, we just need to use the expressions of half life and it's relation with the concentration or mass of a compound. That expression is the following:

A = A₀ e^(-kt)   (1)

Where:

A and A₀: concentrations or mass of the compounds, (final and initial)

k: constant decay of the compound

t: given time

Now to get the value of k, we should use the following expression:

k = ln2 / t₁/₂   (2)

You should note that this expression is valid when the reaction is of order 1 or first order. In this kind of exercises, we can assume it's a first order because we are not using the isotope for a reaction.

Now, let's calculate k:

k = ln2 / 956.3

k = 7.25x10⁻⁴ d⁻¹

With this value, we just replace it in (1) to get the final mass of the isotope. The given time is 1 year or 365 days so:

A = 250 e^(-7.25x10⁻⁴ * 365)

A = 250 e^(-0.7675)

A = 191.87 g

However, the question is the percentage left after 1 year so:

% = (191.87 / 250) * 100

<h2>% = 76.75%</h2><h2>And this is the % of isotope after 1 year</h2>
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