an important concept is for us to think about how we measure our heat changes and what kind of units that we're going to use to do that measurements so the first one is a calorie and this is the the energy it takes to heat one gram of water one degree celsius so this is a definition that is classic in terms of what we use and you will see this come up quite a bit in one particularly common place you will see the term calorie is when you look at your food packaging but recognize that the calorie that is on the packaging is actually with a capital c and the capital c is actually a k calorie so make sure you do understand that in terms of thinking about something that is more real um that you might accomp uh encounter every day but the most common unit that we're going to use is actually in the si unit and that's our joule so in our joule one joule is going to be equal to the units for that is one kilogram meter squared per second squared so that is our typical si unit that goes back to uh killer to mass and and speeds so we will go ahead and use this joule term uh probably the most but you'll also see calories come up on occasion but we're going to go ahead and calculate q in a couple of different ways so our q is how we are going to measure heat in our reactions but we need to go over a couple of different ways of calculating heat so we can calculate heat using a specific heat capacity and this value is actually an intensive property so bringing back from the earlier concept of extensive versus intensive this value doesn't matter how much material or matters there so we can use a specific heat capacity we're going to use a lowercase c from this just so you know um if you talk to a previous student of gen chem one you will also see this as a lower case s for specific heat capacity but our textbook uses a lowercase c so the heat using um a specific heat capacity can be calculated by measuring the mass times the specific heat capacity times the change in temperature so this is our mass specific heat capacity and this temp delta the delta t is t final minus your t initial so the final temperature of the material and then the initial temperature of this material and that makes sense for this uh the specific heat capacity the units for this is going to be joules per gram degrees celsius and that makes sense because our mass will be able to cancel out the grams over here and our temperature change in temperature can cancel out our degrees celsius so then we get joules at the end for our q which are our s i units for measuring heat so make sure you check your units so one thing that comes up quite a bit your mass may be in some other unit so it may be in something like kilograms or um or milligrams and then you'll have to convert it based on whatever your value your lowercase c is and same thing for temperature um it's actually most common to use things like in kelvin but since we're taking a difference in the temperature degrees celsius also works quite well for these kinds of calculations we can also use what we call a heat capacity a heat capacity is is an extensive property and you will most commonly encounter the heat capacity as a capital c and this will be like the heat capacity of an object your textbook goes really uh detailed into this like for example the heat capacity of a small frying pan is different than the heat capacity of a large frying pan just because there's more mass in a large frying pan so but what we will typically use is this heat capacity will come into something that we are going to call a bomb calorimeter and you will see the heat capacity of that object and you know you have a capital c by looking at the units the units for this are going to be joules per degree celsius so notice in there there isn't any mass because it deals with a specific object uh that we are using so the q to calculate for this is going to be our capital c times delta t so we get our joules per degree celsius here and we get our t final minus our t initial so based on these couple of uh definitions we have uh plenty to calculate in terms of our next topic which is going to be calorimeters