In a coffee-cup calorimeter experiment, 10.00 g of a soluble ionic compound was added to the calorimeter containing 75.0 g H2O initially at 23.2°C. The temperature of the water increased to 31.8°C. What was the change in enthalpy for the dissolution of the compound? Give your answer in units of joules per gram of compound. Assume that the specific heat of the solution is the same as that of pure water, 4.18 J ⁄ (g ⋅ °C).

The answer is 269.6 J/g

Explanation:

In a coffee-cup calorimeter, the heat released by the dissolution process of the ionic compound is absorbed by the water. So, heat of dissolution () is equal to the heat of water ().

We can first calculate the heat absorbed by the water:

= m x Sh x ΔT

The specific heat of water(Sh) is known (4.18 J/g.ºC) and m is the mass of water in the calorimeter (75.0 g); ΔT is the change of temperature of water, from 23.2°C (initial temperature) to 31.8°C (final temperature). We introduce the data and calculate :

= 75.0 g x 4.18 J/g.ºC x (31.8°C - 23.2°C)

= 2696.1 J

As we know that heat of dissolution () is equal to the heat of water () have already obtained , and we have to only divide it into the mass of compound (10.00 g). In this way, we obtain the enthalpy change of dissolution in J per gram:

= ΔH/m= 2696.1 J/10.00 g= 269.61 J/g

- calcium has greater affinity to bond with electron receptors than hydrogen does and hence, it has the ability to replace hydrogen in most of its compounds.

- lithium has 2 valence electrons in the product because it can make only 1 bond with hydrogen. beryllium has 4 valence electrons in the product because it can only make 2 bonds. it has fewer electrons than neon and can react with electron donors. each hydrogen has 2 valence electrons, the same as helium.

- the covalent bond formed between carbon and hydrogen is polar because carbon is more electronegative than hydrogen and it attracts the bonded electron pair closer to itself, thus giving hydrogen a partial positive charge.

- a hydrogen bond is a relatively weak bond that hydrogen atoms make with the electronegative atoms nitrogen, oxygen or fluorine.

so the best choice is a.) 2 calcium (ca) atoms