 Let's go through this problem, which is asking us to calculate the lattice enthalpy of potassium bromide and to help us with the calculation, this is some of the data that is given to us. Standard enthalpy of formation of KBr, the standard enthalpy of sublimation of potassium, the standard ionization enthalpy of potassium, the standard enthalpy of atomization of bromine and the standard electron gain enthalpy of bromine. So you can pause the video and give this a try and then we'll continue with the solution. So to start with our calculation, we first look at the information that is given to us and let's start by writing the reactions for which these enthalpies are given. So if we start with standard enthalpy of formation of potassium bromide, we can write the reaction like this and for this reaction, the enthalpy value is known. Now to calculate the lattice enthalpy, we want potassium and bromine ions. So if we first consider the sublimation of potassium, we can write the sublimation reaction like this to obtain the potassium in gaseous form and now since the ionization energy is also given, we can take off an electron and get the potassium ion in gaseous form and similarly for bromine, we can write the reaction for the atomization of bromine liquid into bromine gas and since we know the electron gain enthalpy of bromine, we can extend this to form the bromine ion like this and here we can see that we have the reaction to describe our lattice enthalpy which we can write like this and for each of these steps, the individual enthalpies are known and by Hess's law, we know that the enthalpy change across multiple steps will be equal to their summation so because we know these individual enthalpy values, we can sum up the enthalpy values like this. We can write this equation relating all the enthalpies that are used here and one thing to note here is that the enthalpy of atomization is given as per mole here but when we go from bromine liquid to bromine in the gaseous state, the pre-factor here is half so for this reaction, the enthalpy will also be half the value that is given here and the other thing is when we define the lattice enthalpy, we define it as the energy required to break one mole of a substance into its ions in the gaseous state but the reaction here is in the other direction so while equating the enthalpies, we take this value to be negative and now since each of these values are given, we can just rearrange the terms of this equation to calculate the lattice enthalpy and by plugging in the values along with their correct sign, we get the lattice enthalpy to be 674 kilojoules per mole.