A hot-water bottle contains 791 g of water at 65 °C. If the liquid water cools to body temperature (37°C) how many kilojoules of heat could be transferred to sore muscles?

number of molecules / avogadro's number * molecule molecular = mass

explanation:

we define a gram-molecular weight as the mass of one mole of any element or compound. a mole contains avogadro's number of units (molecules) –  

6.022

x

10

23

. so, dividing the number of molecules by avogadro's number gives us the number of moles. multiplying that by the molecular weight gives us the mass. from the periodic table we find the gram-molecular weight of u to be238 and of f to be19. so,  

u

f

6

will have a gram-molecular weight of 352g.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.