Hess Cycles

How do you know which way the arrows in Hess cycles should be facing?
For example how would i know if the arrows should go from the elements to the reactants or from the reactants to the elements and then to the products?
Thank you so very much in advance!!

How do you know which way the arrows in Hess cycles should be facing?
For example how would i know if the arrows should go from the elements to the reactants or from the reactants to the elements and then to the products?
Thank you so very much in advance!!

Arrow facing depends on whether sth is endothermic (up) or exothermic (down). I think the question tells you about enthalpy change of atomisation or hydration or ionisation energy etc. therefore correspondingly yiu have to jnow your equation first. But it always go from reactants to products.

Generally it helps to know definitions of different kinds of enthalpy changes when making that decision.
Suppose we are required to make a Hess cycle in order to calculate the enthalpy of solution. For this, you will be given the lattice enthalpy of dissociation and the hydration enthalpies of the ions.
By definition, the lattice dissociation enthalpy is the enthalpy change when 1.00 mol of a solid ionic lattice is broken up into gaseous ions, so the relevant arrow should point from the solid ionic compound to the gaseous ions.
Similarly, hydration enthalpies involve 1.00 mol of gaseous ions dissolving in water (to form an infinitely dilute solution) to give aqueous ions. As such, this arrow will point from the gaseous ions to the aqueous ions.

My teacher did say though, arrows face up for formation and arrows face down for combustion

When exactly do you need to use hess cycles in questions? Why can't you just do the bond enthalpies of reactants- bond enthalpies of products?

What exam board do you do? For ocr a they normally only involve formation and combustion

I mean obviously you can do that if the data of the bond enthalpies of the bonds in a compound are given. But you use hess cycles, when that isnt given and enthalpy change of xxx is given .

and is it always reactants- products or is it sometimes the other way round. if it is the latter then how do you know which way round it is?

Am I right in guessing entropy change is second year or a later topic?

Thank you so much, that was so helpful!

ALWAYS reactants minus products for enthalpy
Product minus reactants is only for entropy change.