Atomic number refers to the number of protons within the nuclei of an element's atoms (and therefore the number of electrons) while mass number refers to the number of protons and neutrons within the nucleus.
B. A new material is formed
ιт ιѕ ¢αℓℓє∂ тнє ρα¢ιfι¢ ρℓαтє. ιт ιѕ α σ¢єαиι¢ тє¢σиι¢ ρℓαтє, ιт ℓιєѕ вєиєαтg тgє ρα¢ιfι¢ σ¢єαи
нσρє ι ¢συℓ∂ нєℓρ уσυ συт.
Enthalpy change is the difference between energy used and energy gained. The change in enthalpy of the liquid mercury is 0.0231 kJ.
<h3>What is the enthalpy change?</h3>
Enthalpy change is the difference between the energy used to break chemical bonds and the energy gained by the products formed in a chemical reaction.
The enthalpy change is given by,

and,

Given,
Mass of the liquid mercury (m) = 11.0 gm
The specific heat of mercury (c) = 0.14 J per g per degree Celsius
Temperature change = 15 degrees Celsius
Enthalpy change is calculated as:

Therefore, 0.0231 kJ is the change in enthalpy.
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The mass for of aluminum that is produced by the decomposition of 5.0 Kg Al2O3 is 2647 g or 2.647 Kg
calculation
Write the equation for decomposition of Al2O3
Al2O3 = 2Al + 3 O2
find the moles of Al2O3 = mass/molar mass
convert 5 Kg to g = 5 x1000 = 5000 grams
molar mass of Al2O3 = 27 x2 + 16 x3 = 102 g/mol
moles =5000 g/ 102 g/mol = 49.0196 moles
by use of mole ratio between Al2O3 to Al which is 1:2 the moles of Al = 49.0196 x2 =98.0392 moles
mass of Al = moles x molar mass
= 98.0392 moles x 27g/mol = 2647 grams or 2647/1000 = 2.647 Kg