Couple of questionsssss.

[username]

1. What is the difference between ΔE and ΔH? Doesn't ΔE mean energy released and ΔH mean change in heat? In a question they asked for the "total amount of heat evolved in the reaction", but to find it they used E = m x c x ΔT

2. I read somewhere that the pH of water can change depending on the temperature, is this true? I thought water was always neutral..

3. In galvanic cells, must one of the electrodes by reactive (one of the products) and the other must be unreactive?

4. In Galvanic cells, if zinc is at the negative electrode, will the mass decrease but the Zn2+ concentration increase? Is that always the case, and vice versa at the positive electrode?

5. Ooh and does the object to be plated ALWAYS form on the negative cathode?

Thank you for any help. 

[Mao]

1. ΔE is the change in energy. So burning one gram of coal has a different ΔE to burning two grams
ΔH is the change in energy per mole (or per equation).

2. pH can change, but the water is still neutral. Remember, neutral is when [H+]=[OH-]. When pure water is heated, the percentage ionisation increases, however the two ions still exist in equal ratios

3. nope, consider connecting the Fe2+/Fe3+ half cell (Pt electrode) and the I2/I- half cell (Pt electrode).

4. yes. if zinc is the negative electrode, it is the anode where zinc metal is oxidised.

5. for metal electroplating, yes. look in the electrochemical series, only reduction of metallic ions produce a metal solid. [though beyond VCE, there may be cases against this. but GENERALLY, and for VCE purposes, this is true]

[beezy4eva]

1.not sure... i think they're the same thing
2.pH can change, as pH is a measure of [H+], and water may ionise more or less at different temperatures. However,  [H+]=[OH-] always in pure water irregardless of the temperature.
3.Err mayb try rewording that. Either can be reactive or unreactive, depending on the kind of cell I think.
4. The mass of the Zn(s) will decrease as the Zn(s) loses electrons to form Zn2+, hence increasing the concerntration of Zn2+.
5. Yes, as reduction always occurs at the cathode, so to plate something with metal it must be at the cathode.

[username]

Thanks guys.

[username]

In a question, it asks for the equations if the following react:

Cu / Pb(NO3)2

It says this doesn't react, why?

And:

H2O / Mg

Which water should I refer to for this reaction?

[Collin Li]

In a question, it asks for the equations if the following react:

Cu / Pb(NO3)2

It says this doesn't react, why?

There is no reaction because the lead ions and the copper metal are more stable than lead metal and copper ions (conjugate redox pairs). In other words, if you circled the lead ions and the copper metal on your electrochemical series, you would not get a downwards sloping line connecting them.

H2O / Mg

Which water should I refer to for this reaction?

Check out all of them. See if the reactions are compatible.

[username]

Ohh right. Thanks a lot!