For the reaction: 2 A + B2 --->> 2 AB Triangle H = -30.0 kJ a. The reaction is endothermic.

b. Heat is released to the surroundings.

c. The standard enthalpy of formation for AB is 30.0 kJ.

d. The bond energy for each A-B bond is 30.0 kJ.

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.

answers: to make sure that all of the broken pieces of tablet were added to the water, to allow for fair comparison of all three trials, with different particle sizes to avoid experimental error

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