A calorimeter contains 35.0 mLmL of water at 15.0 ∘C∘C . When 2.20 gg of XX (a substance with a molar mass of 56.0 g/molg/mol ) is added, it dissolves via the reaction X(s)+H2O(l)→X(aq)X(s)+H2O(l)→X(aq) and the temperature of the solution increases to 26.0 ∘C∘C . Calculate the enthalpy change, ΔHΔHDelta H, for this reaction per mole of XX. Assume that the specific heat of the resulting solution is equal to that of water [4.18 J/(g⋅∘C)J/(g⋅∘C)], that density of water is 1.00 g/mLg/mL, and that no heat is lost to the calorimeter itself, nor to the surroundings. Express the change in enthalpy in kilojoules per mole to three significant figures.

ΔH rx = -43.5 kJ / mol

Explanation:

In water, Xdissolves thus:

X(s) + H₂O(l) → X(aq) + H₂O(aq)

It is possible to find the heat in dissolution process using coffee cup calorimeter equation:

Q = -m×C×ΔT

Where Q is heat, m is mass of solution (35.0g -density 1g/mL- + 2.20g = 37.2g), C is specific heat of solution (4.18J/g°C), and ΔT is change in temperature (26.0°C-15.0°C = 11.0°C)

Replacing:

Q = -37.2g×4.18J/g°C×11.0°C

Q = -1710J = -1.71kJ

As enthalpy is the change in heat per mole of reaction, moles of X that reacted were:

2.20g X × (1mol / 56.0g) = 0.0393 moles

As heat produced per 0.0393moles was -1.71kJ, heat per mole of X is:

-1.71kJ / 0.0393mol = -43.5 kJ / mol = ΔH rx

assuming that your periodic table has eighteen columns, you should highlight   the four elements in the third column from the left of the table.

neutral atoms of elements after calcium contain d electrons. the energy of d orbitals of a particular main shell lies between the energy of the s and p orbitals of the next main shell. for example, electrons in the have energy higher than those in the orbital while lower than those of the orbital.

by the aufbau principle, electrons fill orbitals one at a time, starting from those of the lowest energy. the orbital is therefore filled right after orbitals and before orbitals.  

potassium has electron configuration and calcium . the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration and satisfy the requirements.

a neutral atom of the element contains three electrons on top of the most recent noble gas element. it should thus be placed in the third column of the periodic table. both scandium and yttrium would satisfy the conditions. an aufbau diagram indicates that the 4f orbital is filled before the 5d. however, it appears that exceptions exists for both lanthanum and actinium. neutral atoms of the two d-block elements also demonstrate the and should be highlighted as well.

fe 55.85 g/mol and h2o 18.02 g/mol.