Chemistry, 30.06.2019 04:30 Jonah58

40.0 ml of 0.200 m aqueous naoh is added to 200.0 ml of 0.100 m aqueous nahco3 in a flask maintained at 25 ? c. neglecting the effects of dilution, what is q for this reaction?

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Answer from: tiffanyrhoda

Answer : The 'q' for this reaction is, 328 J

Explanation :

First we have to calculate the moles of NaOH and NaHCO_2 .

$\text{Moles of }NaOH=\text{Molarity of }NaOH\times \text{Volume of solution}=0.200mole/L\times 0.04L=0.008mole$

$\text{Moles of }NaHCO_2=\text{Molarity of }NaHCO_2\times \text{Volume of solution}=0.100mole/L\times 0.2L=0.02mole$

From this we conclude that, the moles of NaOH are less than moles of NaHCO_3 . So, the limiting reactant is, NaOH.

Now we have to calculate the 'q' for this reaction.

The balanced chemical reaction will be,

$OH^-+HCO_3^-\rightarrow CO_3^{2-}+H_2O$

The expression used for 'q' of this reaction is:

$q=n(\Delta H_f^o\text{ of product})-n(\Delta H_f^o\text{ of reactant})$

$q=n[(\Delta H_f^o\text{ of }CO_3^{2-})+(\Delta H_f^o\text{ of }H_2O)]-n[(\Delta H_f^o\text{ of }HCO_3^-)+(\Delta H_f^o\text{ of }OH^-)]$

where,

n = number of moles of limiting reactant = 0.008 mole

At room temperature,

$\Delta H_f^o\text{ of }CO_3^{2-}$ = -677 kJ/mole

$\Delta H_f^o\text{ of }H_2O$ = -286 kJ/mole

$\Delta H_f^o\text{ of }HCO_3^-$ = -692 kJ/mole

$\Delta H_f^o\text{ of }OH^-$ = -230 kJ/mole

Now put all the given values in the above expression, we get:

q=0.008mole[(-677kJ/mole)+(-286kJ/mole)]-0.008mole[(-692kJ/mole)+(-230kJ/mole)]

q=0.328kJ=328J (conversion used : 1 kJ = 1000 J)

Therefore, the 'q' for this reaction is, 328 J

Answer from: Quest

the best answer is d because the strong cohesion is caused by the ability of water molecules to undergo hydrogen bonding.

a is incorrect because when water solidifies, it becomes ice, which expands and occupies a bigger volume for the same mass of water in its liquid state.

b is incorrect because water has high surface tension. besides bonding to itself it hydrogen bonds to other molecules at the top decreasing possibility for breaking of attractive forces.

c is incorrect because the water molecule has oxygen which is highly electronegative and so pulls the electron pair towards itself creating a dipole moment, making the molecule polar.

e is incorrect because water has strong adhesion, ability to stick to other molecules such as glass because of this molecules having stronger hydrogen bonding than water.

Answer from: Quest

answer is: naturally occurring solid, inorganic compound or element is mineral.

minerals usually have crystalline form, that means than crystal constituents (atoms, molecules or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions.

for example magnetite is a mineral of iron oxide (fe₂o₃).

calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (caco₃).

dolomite is an carbonate mineral composed of calcium magnesium carbonate (camg(co₃)₂).

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