Now with the internal energy of a system, we have the internal energy formula. We're going to say this formula is used when we have the heat and work of a system. We know that ΔE=Q+W. ΔE is our internal energy. It can be in either joules or kilojoules. Q represents our heat. It can also be in joules or kilojoules. And then W equals work.
Now with work we have an additional formula. Here the work formula is used when we have the pressure and volume of a system. Here work equals negative times delta VS. We're going to say here P equals pressure in atmospheres, V equals volume in liters, and then we're going to say liters times atmospheres is equivalent to 101.325 Joules. Now this is important because if work is given in liters times atmospheres, then we use this conversion factor here to change it into joules.
And we're going to say here, connected to this idea of heat and work is another term, enthalpy, which uses the variable of ΔH. We're going to say it represents the amount of heat released or absorbed during chemical reaction. It should sound kind of familiar to you. We're going to say here that at constant pressure, enthalpy and heat can be treated as the same variable. So at constant pressure, we're going to say here that enthalpy, which is ΔH, is equal to heat, which is Q.
So keep these formulas in mind. Because remember, if it has a purple box around it, that means you're responsible for memorizing it for any upcoming quizzes or exams. So remember internal energy equals Q+W and work equals negative pressure times change in volume.