00:01
If you have a balanced equation and enough information to fill up the q equals m -q equation and solve for q heat, then you can actually calculate the delta h for the reaction, the change in enthalpy for the reaction.
00:15
All right.
00:16
Let's see what some type of information you would need to solve this type of problem.
00:20
So let's say you had a calorimeter, an insulated device that you could measure the temperature change in.
00:26
Imagine there's a thermometer here showing you the temperature change.
00:29
If you had that piece, you could add different things to it, figure out the mass, heat capacity, and change in temperature, and then solve for the delta h of the reaction in a couple steps.
00:44
Let's see how we could do that.
00:47
So let's say your q, your heat energy is equal to a mass times heat capacity times delta t.
00:54
A lot of times you have an aqueous solution.
00:56
So if you had an achilles solution containing hydrochloric acid and zinc, because it's aqueous between it's dissolved and water, the heat capacity is usually very similar to the heat capacity of water.
01:07
All right, so that c is most likely to be very close to the heat capacity of water, which is 4 .18 joules per gram degree celsius.
01:18
When you plug this stuff in a calculator, make sure you have those two things in parentheses because you have to divide by both of them, divide by grams times change in, or the degrees celsius.
01:30
So that's simply your number of you have to divide you have to divide by grams.
01:30
C -dium.
01:32
Your mass would have to be given to you in some way.
01:35
Here's two masses they might give you.
01:37
One they might tell you that, hey, you have a certain amount of zinc.
01:41
You have certain many grams of zinc.
01:42
You have 0 .103 grams of zinc.
01:48
It would be tempting to use that as your mass for your answer, for your your, your, your, your, your, but if i'm talking about this whole system, which includes the zinc and the hydrochloric acid mixing together, i tell you, i tell you, secondly, don't need the mass of just the zinc.
02:04
I need the mass of the whole thing.
02:08
This thing's labeled at 50 milliliters.
02:10
Let's say this whole piece is 50 milliliters.
02:14
The water, or the water, the hydrochloric acid, and zinc, all our reactive pieces are 50 milliliters in total.
02:22
And let's say that the density of that solution is 1 .0 grams per 1 ,000 which makes it basically very close to density of water.
02:34
Basically means that if i had 50 milliliters of this solution, that means i'd also have 50 grams of that solution, that whole solution.
02:46
So that includes the zinc and everything else.
02:51
And let's say the initial temperature of the system was 22 degrees celsius or 22 .5 degrees celsius.
03:02
I'm using this asterisk celsius because i don't have a degree symbol of my computer.
03:07
All right, and the final temperature end up being 23 .7 degrees celsius.
03:17
Based off this information, i could actually calculate the q equals m -cat and then use that information to solve the delta h of a reaction.
03:27
Let's start filling these values in.
03:34
So in this problem, i described us of having a solution of about 50 grams.
03:40
So since there's 50 milliliters and it's one gram per one millimeter, overall the mass of the solution is 50 grams.
03:51
I don't use the 0 .103 grams of zinc because that's only the part of the system.
03:56
The whole system is the zinc and the hydrochloric acid together.
04:00
That's the whole thing that's giving off that heat eventually.
04:04
The heat capacity of the solution is that same as the water of 4 .18 joules.
04:13
4 .18 joules.
04:17
That's per gram per degree celsius.
04:20
Overall, the change in temperature, i start at 22 .5, i went to 23 .7.
04:29
The temperature is increasing, right? i like to do final minus initial.
04:36
In my example here, 23 .7 minus 22 .5 is my change in temperature.
04:46
I could do this math and solve it and simplify it, or i could just plug this all in my calculator.
04:51
A lot of times just for simplicity, i've plugged my calculator.
04:55
One thing to keep in mind, so since i'm starting the grams here and dividing by grams here, those two grams are going to cancel out.
05:04
All right.
05:05
This is change in temperature degrees celsius.
05:08
I'm dividing by degrees celsius here.
05:10
So that degree celsius cancel out.
05:13
And eventually i'll just be left with a amounted jules, a joules energy.
05:16
After i do this math, 50 times 4 .18 times 23 .7 minus 22 .5, which is about, what is that, 1 .2? which is equal to a positive change of 1 .2.
05:31
Positive 1 .2 for my change in temperature.
05:35
All right, let's plug this in our calculator and find our q for the reaction or for the reaction that happened in this system.
05:44
50 times 4 .18 times 1 .2.
05:50
Gives me 250 .8 as my energy change.
05:56
8.
05:57
That is in joules...