Hess’s law is very powerful. It allows us to combine equations to generate new chemical reactions whose enthalpy changes can be calculated, rather than directly measured. Besides that, Hess’s law states that when chemical equations are combined algebraically, their enthalpies can be combined in exactly the same way. Below points are to be taken as well: 1) If a chemical reaction is reversed, the sign on ΔH is changed; 2) If a multiple of a chemical reaction is taken, the same multiple of the ΔH is taken as well. As attached is an example of Hess Law problem solving question. By using Hess law , combine the equation algebraically and determine the enthaphy change of the reaction.  ​

Mass is the amount of matter in an object.  weight is the measurement of the pull of gravity on an object.  say for example, you travel to the moon which has a different gravitational field compared to the gravitational field of earth. (gravitational fields: earth = 1, moon = 0.165)  now when you are on the moon, the pull of gravity on you is different than on the earth. and as weight is the measurement of the pull of gravity on an object, that means yes, your weight can and will change on the moon.  however, on the moon, on earth or even on jupiter, the amount of mass inside of you remains the same. meaning your physical mass remains constant.  in conclusion it is possible for your weight to change as your mass remains constant. 

Ibelieve the answer 4 moles