# Make Ex 5 Notes

Jan 7, 2012
117
Here's what I wrote down in my notes for MAKE ex 5. I haven't memorized it yet, but I am thinking of making flashcards for it. Here are my notes:

-When zinc reacts chemically with an acid, it can liberate electrons

-Electrons want to leave without other electrons joining them (aka mutual repulsion)

-When a wire connects the zinc electrode to another electrode with an shortage of electrons, the electrons move from one atom to the next to go from zinc electrode and run through wire

-more electrons reduce previous ones in the process until zinc-oxide reaction grinds to a halt

-primary battery = a battery ready to generate electricity the second there is a connection between its terminals

-when raw metal in electrodes is used up, the battery dies

-emitting electrons = to send electronics

-Negative electrons flow from positive to negative

- 1 amp = 1 coulomb/second

-coulomb = unit of electrical potential

-1 newton = the force required to accelerate 1 kilogram by 1 meter per sec

-1 joule = a force of newton acting through 1 meter

-chemical reactions inside batteries change pure metals into metallic compounds which enables power
-this process can be reversed

-2 batteries in series deliver twice as much voltage

-2 batteries in parallel deliver twice as much current

Also, does the potential difference determine how long the electricity will flow until both sides of the battery are equal? I'm just asking because I happened to think of it writing this.

I'm going to make flash cards out of these so I wanted to know if they were okay. Thanks for the replies.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
That's pretty good.

I think there are a few improvements we can make...

Here's what I wrote down in my notes for MAKE ex 5. I haven't memorized it yet, but I am thinking of making flashcards for it. Here are my notes:

-When zinc reacts chemically with an acid, it can liberate electrons
I'll go along with that.
-Electrons want to leave without other electrons joining them (aka mutual repulsion)
This one is a bit tricky. You'll have to explain where you got this from. As it stands, it needs improvement, I'm just not sure what way it needs to go.
-When a wire connects the zinc electrode to another electrode with an shortage of electrons, the electrons move from one atom to the next to go from zinc electrode and run through wire
That seems OK
-more electrons reduce previous ones in the process until zinc-oxide reaction grinds to a halt
The first part of this is a bit messy (where do you get this from) but the second is essentially correct. When there is no more material left to react, the reaction cannot continue and the battery is indeed flat.
-primary battery = a battery ready to generate electricity the second there is a connection between its terminals
Hmmm... primary batteries are manufactured in a charged state and normally cannot be recharged. It is designed to be used once (or until flat) and then discarded
-when raw metal in electrodes is used up, the battery dies
it's not always raw metal, although it may well be.
-emitting electrons = to send electronics
Not completely sure what you mean here. If you mean that the electrons which are forced out of a battery are sent along wires to power electronic devices, then yes, but it's not so much the electrons themselves as it is the force which pushes them that we're interested in.
-Negative electrons flow from positive to negative
They do! (outside of the battery)
- 1 amp = 1 coulomb/second
yep
-coulomb = unit of electrical potential
it's actually a unit of charge, essentially the equivalent of a number of electrons
-1 newton = the force required to accelerate 1 kilogram by 1 meter per sec
yep
-1 joule = a force of newton acting through 1 meter
it is also 1 watt expended for a period of a second (Watts are Joules per second.)
-chemical reactions inside batteries change pure metals into metallic compounds which enables power
generally speaking they change one substance into another in a way that releases energy. A metal to a metal oxide is one of these -- essentially you're burning metal, and burning releases energy.
-this process can be reversed
often, but not always. Turning a metal oxide back to a metal requires the addition of energy. Inside a battery you may not be able to do this. The ability to do this is generally a marker of what makes a cell primary or secondary.
-2 batteries in series deliver twice as much voltage
they do
-2 batteries in parallel deliver twice as much current
that too!
Also, does the potential difference determine how long the electricity will flow until both sides of the battery are equal? I'm just asking because I happened to think of it writing this.
not really. in your examples above, the batteries would go flat after the same amount of energy was taken out. Energy is power time time. if we want to do it in the same time we need to keep the power the same. And since power is voltage times current, we need to draw half the current when the batteries are in series as we do when the two of them are in parallel. In this case, you can draw a higher current for longer from the LOWER voltage collection of batteries. This is (one reason) why you place batteries in parallel, to allow you do draw more current.
I'm going to make flash cards out of these so I wanted to know if they were okay. Thanks for the replies.
Maybe we can get you some slightly better wording. See what others have to say.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
(Watts are Joules per second.)/QUOTE]

Other way around. A Joule is a Watt second.

http://en.m.wikipedia.org/wiki/Joule

You are, of course, exactly right. I'll edit for my brain fart

Hang on, I said "Watts are Joules per second". "Joules are Watt seconds" is an equivalent statement.

J = W.s

=> J/s = W.s/s .... (for s <> 0)
=> J/s = W

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Aug 13, 2011
1,114
Hang on, I said "Watts are Joules per second". "Joules are Watt seconds" is an equivalent statement.

J = W.s

=> J/s = W.s/s .... (for s <> 0)
=> J/s = W

Nice try with sophistry. It's more a matter of convention and definition than of mathematical manipulation anyway.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Nice try with sophistry.

I'm not sure what you mean. A Watt *IS* a Joule per second.

See here:

The watt (
/ˈwɒt/ WOT; symbol: W) is a derived unit of power in the International System of Units (SI), named after the Scottish engineer James Watt (1736–1819). The unit, defined as one joule per second, measures the rate of energy conversion or transfer.

Anyway, I'm sinister, not sophist.

#### davenn

Moderator
Sep 5, 2009
14,085
-primary battery = a battery ready to generate electricity the second there is a connection between its terminals

no, not an accurate definition, as that would include rechargables
In addition to what steve said -- the other standard meaning for primary is in the term

Primary Cell like your 1.5V cell size AAA, AA, C, D or those big 1.5 volt ones used in the old telephone systems etc

they are not BATTERIES a Battery is a collection of CELLS
its just that everyone has got use to calling AAA, AA etc cells batteries but technically its incorrect

your small 9V batteries ARE batteries if you open a dead one up, you will find its made of of a number of cells. A car battery is also a real battery as it is also a collection of cells

-when raw metal in electrodes is used up, the battery dies
-

no not really, infact probably very rarely. The battery/cell dies - goes flat when the chemical reaction can no longer be sustained. Take a AA cell, it has only 1 metal electrode ... the zinc casing ... when the battery is flat, that zinc casing is still very intact
definately NOT used up
the other electrode is a carbon rod, it is centred down the middle of the cell and the area between it and the zinc case electrode is filled with a chemical compound

cheers
Dave

Aug 13, 2011
1,114
A Watt *IS* a Joule per second.

You're right. I've only seen it described the other way (Joule = Watt second).

#### wingnut

Aug 9, 2012
259
I really like the whole logical flow diagram, connection of thoughts that you have going on.

The only things I would question are...

-more electrons reduce previous ones in the process until zinc-oxide reaction grinds to a halt

-Negative electrons flow from positive to negative

As I understand it, conventional current (holes) flow from positive to negative, but "negative electrons" flow from negative to positive (outside the cell). This makes logical sense since why would negative electrons want to flow away from the positive (electrode) since they are attracted to the positive?

At the zinc electrode (not zinc-oxide??) zinc undergoes oxidation.
Zn ---> Zn++ plus 2e-........... which leaves the outer zinc casing negative.

At the other electrode (cathode- usually a carbon rod surrounded by manganese dioxide) reduction occurs, leaving the carbon net positive.

I don't understand what you meant by "more electrons reduce previous ones in the process" - what were the "more electrons" and what were the "previous ones" and for that matter, what was "the process"? This just needs a little clarification. Why I say that is because electrons cannot reduce electrons. Reduction is defined as where some substance gains electrons. Electrons cannot gain electrons since where would they put these

But a great collection of important concepts well worth committing to flash cards.

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