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zvonat [6]
3 years ago
12

HELP PLEASE I GIVE 21 POINTS!!!! +BRAINLIEST!!!!!!!

Chemistry
2 answers:
Maslowich3 years ago
8 0
There was a noise in my closet one night and it creeped me out. It scared me until I told myself that it might not be so scary if I checked it out. When I got to the closet, my heart pounding, I realized that it was just a book that had fallen off the shelf. 
cricket20 [7]3 years ago
7 0
You could write about a fear you may have had as a child, eg. the dark, or underneath the bed, etc...
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What era is know as the age of mammals?
kondaur [170]
The <span>era that is know as the age of mammals is the </span><span>Mesozoic period.

Answer: Letter D

Hope that helps. -UF aka Nadoa</span>
7 0
3 years ago
Which unit can be used to express the rate of a reaction?
vichka [17]
<span>The rate of reaction may be expressed as a unit of quantity divided by a unit of time. The only expression that has a quantity divided by time is the first one mL / s (i.e. milliliter per second), so the answer is the first option, mL/s.</span><span />
4 0
3 years ago
Read 2 more answers
Differentiate between compounds and mixtures using the particle model of<br> matter.
trasher [3.6K]

Answer:

compounds are substance which can be formed by chemically combining two or more elements.

mixtures are substance that are formed by physically mixing two or more substances

8 0
2 years ago
What is the E°cell for the cell represented by the combination of the following half-reactions? ClO4–(aq) + 8H+(aq) + 8e– Cl–(aq
Vinvika [58]

Answer:

The E°cell for the cell represented by the combination of the given half-reactions is 0.398 V

Explanation:

Oxide-reduction reactions, also called redox, involve the transfer or transfer of electrons between two or more chemical species. In these reactions two substances interact: the reducing agent and the oxidizing agent.

The gain of electrons is called reduction and the loss of electrons oxidation. That is to say, there is oxidation whenever an atom or group of atoms loses electrons (or increases its positive charges) and in the reduction an atom or group of atoms gains electrons, increasing its negative charges or decreasing the positive ones.

The species that supplies electrons is the reducing agent (that is, it is that species that oxidizes, yielding electrons and increasing its positive charge, or decreasing the negative one causing the reduction of the other species) and the one that gains them is the oxidizing agent ( that is, it is that species that is reduced, capturing electrons and increasing its negative charge, or decreasing its positive charge, causing oxidation of the other species).

This is the type of reaction that occurs in this case.

ClO₄⁻(aq) + 8 H⁺ (aq) + 8 e⁻ ⇔ Cl⁻ (aq) + 4 H₂O(l) E° = 1.389 V

VO₂⁺(aq) + 2 H⁺(aq) + e⁻ ⇔ VO⁺(aq) + H₂O(l) E° = 0.991 V

In this case both are written as reductions, and their E ° values ​​as well. The species that has the greatest potential for reduction will be the species that will be reduced, that is, it will be the oxidizing agent. In this case, it will be the first half-reaction expressed.  Therefore, to obtain a reaction, the second semi-reaction must be reversed to be an oxidation, maintaining its constant value. Then:

Reduction: ClO₄⁻(aq) + 8 H⁺ (aq) + 8 e⁻ ⇔ Cl⁻ (aq) + 4 H₂O(l) E° = 1.389 V

Oxidation: VO⁺(aq) + H₂O(l) ⇔ VO₂⁺(aq) + 2 H⁺(aq) + e⁻ E° = 0.991 V

<em>E°cell=Ereduction - Eoxidation</em>

E°cell=1.389 V - 0.991 V

<em>E°cell=0.398 V</em>

Then <u><em>the E°cell for the cell represented by the combination of the given half-reactions is 0.398 V.</em></u>

Another way of thinking is that, by inverting the second semi-reaction to be an oxidation, the value of E ° is reversed in the sign, unlike the previous case in which it was constant. Then:

Reduction: ClO₄⁻(aq) + 8 H⁺ (aq) + 8 e⁻ ⇔ Cl⁻ (aq) + 4 H₂O(l) E° = 1.389 V

Oxidation: VO⁺(aq) + H₂O(l) ⇔ VO₂⁺(aq) + 2 H⁺(aq) + e⁻ E° = -0.991 V

In this case:

E°cell=Ereduction + Eoxidation=

E°cell=1.389 V + (-0.991 V)=1.389 V-0.991 V

<em>E°cell=0.398 V</em>

Note that the result obtained is the same. This indicates that either of the two ways proposed is correct, and you will use the one that is most comfortable for you.

4 0
3 years ago
A laser pulse with wavelength 545 nm contains 4.85 mJ of energy. How many photons are in the laser pulse?
dusya [7]

<u>Given</u>:

Wavelength (λ) of the laser pulse = 545 nm = 5.45 * 10⁻⁹ m

Total energy of pulse = 4.85 mJ

<u>To determine:</u>

The number of photons in the laser of a given energy

<u>Explanation:</u>

Energy per photon (E) = hc/λ

where h = planck's constant = 6.626 *10⁻³⁴ Js

C = speed of light = 3*10⁸ m/s

λ = wavelength

E = 6.626 *10⁻³⁴ Js* 3*10⁸ms-1 /5.45 * 10⁻⁹ m = 3.65 * 10⁻¹⁹ J

Now,

# photons = total energy/Energy per photon

                 =  4.85 * 10⁻³ J* 1 photon / 3.65 * 10⁻¹⁹ J = 1.32 * 10¹⁶ photons

Ans: the laser pulse contains 1.32 * 10¹⁶ photons

3 0
3 years ago
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