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Write a balanced equation for the confirmatory reaction or reactions for each cation, when using Ag+, Cu2+, Zn2+, and Ca2+ Ions, Page 93 at Wayne County Community College'

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Write down the equation for the formation of the complex trans-K[Cr(C2O4)2(H2O)2.3H2O from the reactants K2Cr2O7 and H2C2O4.2H2O.

limiting reactant:
The limiting reagent, or also called the "limiting reactant", is the chemical that determines how far the reaction will go before the chemical in question gets used up, causing the reaction to stop. The chemical of which there are fewer moles than the proportion requires is the limiting reagent.

Limiting reagent formula
There is a much simpler formula which can be used. However, you must first calculate the moles of both of the reagents in the reaction. Once the number of moles have been figured out, just simply fill in this equation (reagent 1 being the first reactant and 2 being the second):

When the answer to the formula is less than zero, reagent 1 is the excess reagent. When the answer is larger than zero, reagent 1 is the limiting reagent. The number shows how much in excess one reagent is from another. If the answer for the formula is zero, both reagents are perfectly balanced. The unit of an answer is in moles.

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Estimate the bond energy' S-F' in SF6.the standard enthalpy of formation of SF6(gas),S(g),F(g) are-1100kj/mole,275kj/mole,80kj/mole respectively

What is the S-F bond energy in SF6 given DHfo for each of the reaction components?

For this problem you must first calculate the change in enthalpy (heat transfer, delta H under standard conditions) for the conversion, S(g) + 6F(g) => SF6(g) OR for the reverse reaction, it really doesn't matter, because the numerical value will be the same, regardless. Once you calculate the heat transferred, you will be able to say that the amount of heat transferred was the amount of potential energy trapped in all of the S-F bonds, all six of them in the molecule. So, to obtain the answer asked for (the energy content on one S-F bond), all you will have to do is divide by 6.

The above is a logical approach, because all six of the S-F bonds are identical. This is so, because, according to VSEPR theory (look it up for more background on that, if you are interested), you can predict that its molecular geometry is "octahedral" with the central sulfur atom having "sp3d2 hybridization."

Here is how you set up the problem:

First write the balanced chemical equation with the given heats of formation (in kJ) written under each of the reaction components:
S(g) + 6F(g) => SF6(g)
275 6(80.) -1100.

Note: I am assuming that each of the above quanties is good (i.e., known) to at least the unit's place; that is, + or - 1 kJ. This reasonable assumption allows me to unambiguously indicate the number of sig figs in each quantity - an important consideration for proper rounding off of the final answer.

Recall that the sum of the product values minus the sum of the reactant values, each component multiplied by its corresponding coefficient will give the net enthalpy ("reaction enthalpy") of the reaction as written. In this case, there being only one product, the reaction enthalpy is:
-1100 - (480 + 275) = - 1855 kJ. From this, we can see that as S and six Fs are combined, 1,855 kJ of heat are released into the surroundings (that is, an exothermic reaction). The amount of heat released informs you of the combined bond energy of ALL six S-F bonds.

A good rule to remember: As bonds are formed, energy is always released (an exothermic process). As bonds are broken (as in the reverse reaction), the same amount of energy is being absorbed (an endothermic process).

Therefore, in conclusion, one S-F bond has a bond energy of 309.17, which is more properly rounded off to 309 kJ.

Recall that the rule for rounding off when adding or subtracting is to make sure that the final answer has the same precision as the values used to calculate it. Since each given value was good only only to the last unit

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What is lattice enthalpy

The lattice enthalpy for a particular ionic compound is defined as DH for the process image636.gif. This cannot be measured directly as it is not possible to get this reaction to happen on its own, without many other reactions happening around it. Separate ions cannot be brought together in this way.

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I have a doubt whether that in presence of tap water or salt water or air the nail gets rusted fastly

The short answer is Yes, it does. The reason is, because "salt" (NaCl) is a strong electrolyte, which facilitates the flow of electrons in a naturally produced mini-circuit on the surface of the nail, which is in contact with both air (oxygen) and moisture (water).

The "mini-circuit" mentioned above is the consequence of the kind of reaction (oxidation and reduction occurring simultaneously, called a redox reaction) that an uncharged metal atom (like iron, Fe) can undergo because of its ability to lose its valence electrons (loosely held) that normally move around the outermost orbital of its nucleus. This kind of electron transfer spontaneously occurs (i.e., by itself without any outside help) only if the iron is able to come in contact with an atom of another element, or the ion of that other element (which can be a metal or not), that has an attraction for electrons (standard reduction potential) that is stronger than the attraction of electrons by the iron. For a more detailed and technical explanation, please see my "Solution 2" for this problem.

What's salt got to do with all this?

An electrolyte (pronounced, electro-lite), is so-named because it is a substance that can conduct electricity (electric current). Strong electrolytes (salts) dissolved in water, melted (molten) electrolytes (in absence of water), and pure metals are good electrical conductors*. What makes a strong electrolyte able to conduct electricity is its ionic nature, that is, its being made up of ions, which have charges. When NaCl ("salt") is dissolved in water, it immediately breaks up (dissociates) into its constituent ions (Na+ and Cl-). It's these ions that make the solution a good conductor. So, the more ions in aqueous solution, the more effective the solution can support the flow (transfer) of electrons (current) that are involved in the type of reaction (redox) occurring in the rusting of a nail.

*Exactly how these substances are able to act as conductors has been described in complex theories, but most chemistry textbooks omit them, except for how metals behave as conductors - see more about this using the key search term, electron-sea model, a very well developed theory of metallic bonding. Probably, one of the most essential characteristics of a good conductor is the mobility of its charged particles. For example, though a solution of ions is a good conductor, the pure solid form of the same electrolyte behaves as a non-electrolyte! So, it is reasonable to deduce that when an electron contributes to an electron current going through a solution of ions, it hops a ride on those charged particles, or that the very rapid collisions between them are very effective in allowing virtually instantaneous net electron movement across them.

You also asked about the effect of tap water. See my Solution 2 for this problem.


Aug 26, 2010 | Scientific Explorer My First Chemistry Kit

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Which of the on reacting with ferrous sulphate(FeSO4) will give a black residue? a) Zn ; b) Al ; c) Fe ; d) Cu

What an interesting question! You are asking "Which [of the listed metals] on reacting with FeSO4 will give a black residue?

My answer is None of them - but possibly from either a) Zn and b) Al under certain conditions as indicated below.

Both elemental zinc and aluminum will undergo a redox (reduction-oxidation) reaction with the Fe2+ ion (of FeSO4) to give zinc and aluminum ions (Zn2+ and Al3+), which would form the zinc and aluminum salts, ZnSO4 and Al2(SO4)3 - both of which are white solids. The other product in each of these reactions is elemental iron, which is reported to be silvery, if the iron is free of contaminants). Pure elemental iron is not black. If the freshly formed iron is oxidized, it would probably from iron oxide, Fe2O3, which is "rust," which is reddish-brown, and not black.

HOWEVER, if the above elemental iron becomes colloidal in the presence of impurities (e.g., organics), it is possible that the iron might appear to to be a black residue. And this could occur from the reaction of FeSO4 with either a) Zn or b) Al.

Elemental iron (Fe) will not react with FeSO4, because there would not be any other metallic reactant present that could either oxidize or reduce it.

Finally, elemental copper (Cu) and FeSO4 would not undergo a spontaneous redox reaction written as follows: Cu + Fe2+ => Cu2+ + Fe, no reaction. (Only the reverse reaction would occur: Cu2+ + Fe => Cu + Fe2+, but the problem does not indicate the presence of either Cu2+ or Fe in choice d.)

Jun 27, 2010 | Scientific Explorer My First Chemistry Kit

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I can not set up my DVD, no reaction to remote control, no reaction manual bottons.
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Battery or charger?

battery. call tech support and they will replace.

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