Measuring the Latent Heat of Fusion for Ice: A Comprehensive Experiment Guide

good morning today we are going to do an experiment or a mini lab

that involves measuring the latent heat of fusion or of melting that's our objective today to measure

the latent heat of fusion or melting for ice so what is latent heat it's defined as the energy absorbed

or released by a substance during a change in state specifically fusion refers to when a

solid melts or a liquid freezes now for ice this value is 334 joules

per gram or 334 kilojoules per kilogram so what does this actually mean what

does 334 joules per gram mean when ice is at 0 degrees celsius

to completely melt one gram of ice requires 334 joules

of energy that's what it means and if you understand what that means then you don't even need a formula

and so here's the question if one gram requires 334 joules what if you have 2 grams of ice how much

energy is required that's correct 334 plus 334 equals 668 joules of energy

so this is our objective today to see if we can come up with an experiment to accurately measure this value in

other words to try to get 334 joules per gram that's our objective so how are we going to do this well as

you saw at the beginning of the video we're going to take some ice and we're going to place it in

warm water the energy to melt the ice will come from the warm

water of course when you put ice and water it's going to cool

and eventually the ice will completely melt here's the key we are going to measure

the change in temperature of the water this will help us measure the energy required to melt the ice

now there's a formula we're going to have to use today to determine the energy required to melt

the ice mass times the specific heat capacity of water

times the temperature change if you're not familiar with this formula please watch this video as this video

reviews the use of that formula this is the table you will need to fill

out today in fact you will need two copies so please make two separate copies of this

table notice we have the water that was originally warm

so we have to account for and this is very much like accounting we have to account for the energy from

the water that was originally warm in the cup however once the ice melts well it leaves water

we also have to account for the water that resulted from the melting of ice and that melting of ice that water was

originally at zero degrees celsius and so let's start off trying to fill

out the table we know this value as listed on the internet is 4.2 joules per gram degree

celsius now let's fill out the trial here's trial a we're going to all do

trial a together and i'm going to assist you with the actual calculations for trial a

so please in your title copy down trial a and let's start off with the mass

every trial will have a pitcher just like this notice if you look at the graduated

cylinder it's above 45 mils and that's what our balance is showing us 45.4

grams of water so we complete that entry in the table now the mass of the ice

there's the mass of the ice every trial will start off with a pitcher like this 5.1 grams

all right let's continue the initial temperature the initial temperature and all

temperatures in fact will be recorded with this probe this probe is attached to this device

and this device will output the temperature there it's reading 35.4 degrees celsius

this is very important you want to record the temperature just before the ice was added

to the cup just at that point you're going to see the ice going into the cup that's when you record the temperature

so there's our initial temperature the initial temperature of the ice we're going to assume at zero degrees celsius

because the ice had already started melting even before i put it on the scale i left

the ice out of the freezer for at least 10 to 15 minutes

so there's our entry of the initial temperature the final temperature well the final

temperature for both the water that was originally warm and the water that resulted from the

melting of ice is going to be the same and so here we go we're going to take

our ice place it in the water and after the ice is completely melted in the cup of water we're going to

record that final temperature let's now review the video to record the final temperature

so you want to record the temperature it was 35.4 and now notice i'm going to use the

probe to stir the ice around in the water i'm doing that because i want to make

sure that the water's temperature is the same throughout the entire cup now it's a

small amount of water however by stirring we're trying to move that ice around so that it equally cools

the water everywhere so we still have some ice however as you can see it's getting smaller

and of course you can see the temperature dropping it's almost gone the ice

and now at this point i'm really stirring the water to ensure that the temperature is the same

everywhere now it looks like it's the same everywhere i'm moving the probe around

to ensure that all right so there's our final temperature our final temperature is

around 24.5 degrees celsius so we enter that in the table now i just want to come back to the mass

for a moment notice the mass was originally 5.1 grams however immediately after we removed the

ice there was still 0.1 grams left over why is that well notice that the ice

melted slightly leaving some water behind as a result we're going to adjust the

mass and make it 5.0 because we left 0.1 grams of the ice on the scale so instead of writing 5.1

please write 5.0 ensure that when you get your own trial a little later on the video

that if there is this adjustment that takes place that you make that adjustment

all right how do we get the temperature change well there's our formula final subtract

initial temperature and there it is please show your work for this

calculation and now the heat energy there is our formula for heat

energy mass time specific heat capacity times the temperature change and so let's complete that calculation

and please show your work for those two calculations i just illustrated

all right here's our primary formula that's going to help us ultimately get the value that we're

interested in the latent heat of ice it's really a statement of energy

conservation on the left side of the equation we have the energy related to cool the

water that was originally warm and where does that energy come from on the right side of the equation

it comes from the ice that's melting and then the resulting water from the ice that is melted that is now

going to be warmed we will assume the system is closed that means that we're assuming there is

no energy loss or gain with the surroundings primarily with the air

now why is this valid well the experiment only lasts a few minutes that's why it's valid

so there isn't a very long time frame for the cup of water to exchange energy with its surroundings

this was one of the reasons why we used warm water and not room temperature water

by using warm water the ice melted faster which decreased the amount of time of

the experiment the second assumption is that the energy related to cooling the cup is close to

zero of course the cup also gets cooler but we're assuming that that value is close

to zero now why are we allowed to make this assumption well notice the mass of the

cup it's only around 1.6 grams when we compare that to water and ice

that's 50 grams it's a tiny amount of mass in comparison to the water

in addition the specific heat capacity of the cup is probably around two to three times less

than the water so for those two reasons we're going to basically assume it is zero

however you're going to see from the results that with this assumption that it is close to zero

the overall energy that we still get very accurate results so it's a reasonable assumption based on

that all right how do we get the energy to cool the water

well it's this value here and so we substitute that value and remember that two negatives make a

positive and we're left with this how do we get the energy to warm the ice

water well that comes from this value here and so we substitute that value and we

take the difference so the energy required to melt that piece of ice was exactly that value

there and now we know that in order to determine the latent heat of melting

remember the unit is joules per gram so there's our formula for the energy required to melt the ice it's the mass

of ice multiplied by the latent heat of melting and so we have to enter our mass of ice

and there's the mass of ice and now we divide and we'll end up with the unit of joules

per gram and that's the unit that we ultimately wanted and so your goal is to determine the

latent heat of melting based on this equation i want it with the correct units

i also want the correct number of significant digits and figures in addition i want you to calculate the

percentage difference which is the latent heat subtract 334 334 is the actual value for the latent

heat the latent heat is the value we got in this experiment

multiply by 100 this symbol here means absolute value so if you get a negative value when you

take that difference then automatically make it positive percentage differences always have to be

positive finally in your table initially i wrote this number without significant digits

but of course in the table i want you to write this number with the correct number of significant figures or

significant digits all right now on to part two of the experiment

each of you will get your own trial letter there are 10 different letters in total

and each of you will get only one of those letters and you will do the exact same calculations that we

just did except for your own trial so please be sure to indicate which

trial you have been assigned again these are the two goals to get the latent heat of melting and to

get the percentage difference all right here's the information for trial b

here's the video for trial b remember to record the temperature just before the ice enters the cup

the process i'm using will always be the same i will simply be stirring the ice to spread the heat

evenly and of course we have to wait for the entire ice cube to melt

you can always simply forward the video until you see the ice cube melted if you don't want to watch me stirring

the ice still tiny piece of ice there and now basically i'm trying to ensure

that the water is the same temperature everywhere all right trial b has ended

here is trial c please record the mass um and trial c has ended here is trial

d please note the initial temperature and the mass

and like the other experiments i will stir the ice until it's completely melted

so that the heat is evenly distributed so the temperature is the same everywhere in the water and the heat

energy is evenly distributed it's almost completely melted please record the final temperature for

d trial e there's the mass initial temperature mass of the ice

and now we begin to stir you please record the final temperature

trial f please record the mass please record the mass of the ice and the initial temperature as well

note the 0.1 grams left on the scale you please record the final temperature

trial g the mass mass of the ice initial temperature the rapid stirring at the end is to

ensure the water is the same temperature throughout please record the final temperature

trial h the mass note the original mass and note the original temperature

prior to the ice entering the water so you may have to go back and watch that part of the video again

you may have to pause it as well please also note the decimal point one grams

left on the scale still some ice left now the rapid stirring is to ensure that

the water's temperature is the same throughout please record the final temperature

trial i the original mass please record the mass of the ice and the initial temperature

please note that 0.1 grams was left on the scale this is one of the larger pieces of ice

used in the experiment so it's going to take a little longer for it to melt completely

please record the final temperature trial j there's the mass mass of the ice please record and the

initial temperature please note that 0.1 grams was left on the scale

please record the final temperature and finally here's our last trial trial k please record the mass

the original mass of the ice and the original temperature prior to the ice entering the water

please note that decimal 0.2 0.2 grams has been left on the scale so take that into account when you

record the mass of the ice by stirring the ice we're trying to ensure that the heat

is evenly distributed that the temperature of the water is the same throughout the sample

once the ice is completely melted stir the sample of water a bit more to try to ensure that once again the

temperature is the same everywhere please record the final temperature and

so this concludes our experiment today hopefully when you do all your calculations you

get a value for latent heat that is very close to 334 joules per gram you should as i checked

all this data myself prior to creating the video every experiment will give you a value

very close to that value so hope you enjoyed today's lesson and experiment

have a great day bye bye