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Vadim26 [7]
4 years ago
5

Typical residential shower controls mix streams of hot water (140 F, or 60 C) with cold water (60 F, or 15 C) to form a stream o

f 40 C (104 F) water. The entire system loses energy to the surroundings at a rate of 5 kJ/kg of exiting water. What is the ratio of cold water-to-hot water mass flow rates necessary to provide the 40 C water?
Chemistry
1 answer:
sammy [17]4 years ago
3 0

Answer:

  4:5

Explanation:

Let x represent the fraction of the mix that is hot water. Then the temperature of the mix is ...

  60x +15(1-x) = 40·1

  45x = 25 . . . . . . . . . subtract 15

  x = 25/45 = 5/9 . . . divide by the coefficient of x

This is the fraction that is hot water, so the fraction that is cold water is ...

  1-5/9 = 4/9

The ratio of cold to hot is ...

  cold : hot = (4/9) : (5/9) = 4 : 5

_____

<em>Additional comments</em>

The problem assumes that the energy contained in a given mass of water is proportional to its temperature. That is almost true, sufficiently so that we can reasonably use that approximation.

If heat loss is figured into the problem, then additional information is needed regarding the energy content of water at temperatures in the range of interest. That is not provided by this problem statement, so we have ignored the heat loss.

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What three (3) factors determine the reactivity of elements? Explain and give examples of each.
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Explanation:

The three factors which determine the reactivity of elements are as follows.

(1) Number of valence electrons.

(2) Size of an atom.

(3) Electro negativity of an atom.

All these factors are explained as follows.

(1) Number of valence electrons

According to the octet rule, every atom requires to attain stability. Therefore, number of electrons in the outermost shell will decide the reactivity of an atom as every atom needs to fill its shells or sub shells as per the octet rule. As a result, the reactivity increases.

For example, the atomic number of chlorine is 17 and its electronic configuration is 1s^{2}2s^{2}2p^{6}3s^{2}3p^{5}

In the 3p sub shell, there is deficiency of one electron. So, in order to attain stability chlorine atom will react readily with another species or atom which can either donate or share one electron.

Whereas an atom with completely fill shell will have low reactivity.

(2) Size of an atom

On moving down the group size of atom increases. As a result, the attraction between the nucleus and electrons decreases due to the shielding effect. Thus, the larger is an atom, the more easily it can give electrons. Therefore, the reactivity increases.

For example, the atomic number of calcium is 20 and its electronic configuration is 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}

Also it is known that first shell of every atom can have 2 electrons, second shell can have 8 electrons, third shell can have 18 electrons and so on.

Since, calcium is larger in size as compared to beryllium and magnesium so it will readily loose 2 electrons to attain stability. Thus, it will attain a Ca^{2+} charge.

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So, in order to gain stability fluorine will readily accept 1 electron to completely fill its 2p sub shell. As a result, the electronic configuration will become 1s^{2}2s^{2}2p^{6}

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7 0
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When electrolyzing copper (ll) chloride, what reaction takes place at the anode? What reaction takes place at the cathode?
klemol [59]

Answer:

Copper ions are reduced into copper atoms.

Cu²⁺₍aq₎ + 2e⁻ →  Cu₍s₎

Explanation:

During electrolysis,  the positive H⁺ and Cu⁺ ions move to the negative cathode and negative OH⁻ and Cl⁻ ions move to the positive anode.

At cathode, copper ions are preferentially discharged due to the low electromotive force required to discharge them compared to the hydrogen ion. The copper ions gain the two electrons lost by the chloride ions when the are discharged. (2 Cl⁻₍aq₎ → Cl₂₍g₎ + 2e⁻)

Thus the half equation is as follows:

Cu²⁺₍aq₎ + 2e⁻ →  Cu₍s₎

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