Question

1) If dissolving 10.0 g of ionic salt causes 100.0 mL of water

to increase temperature by 24.0 oC at constant
pressure, what would be the change in temperature if 3.33 g of the
same ionic salt were used instead? Assume the volume of solution
remains the same.
2) If a reaction causes 100.0 g of water to decrease
temperature by 13.0 oC at constant pressure, what
is the change in enthalpy for
the reaction? (The specific heat
capacity of water is 4.184 J/g oC). Assume no heat
transferred to surroundings.

Answer 1

To find the temperature change when dissolving 3.33 g of an ionic salt, divide the original temperature change (24.0 °C with 10.0 g) by 3, yielding 8.0 °C. The change in enthalpy for a reaction where 100.0 g of water decreases in temperature by 13.0 °C is -5.428 kJ.

Step-by-step explanation:

To determine the change in temperature for dissolving 3.33 g of an ionic salt, we presume the process is directly proportional to the mass of the salt dissolved in the water since the volume of water stays constant.

Therefore, if dissolving 10.0 g of salt increases the temperature by 24.0 °C, then dissolving 3.33 g of salt, which is ⅓ the original amount, would result in ⅓ the temperature change. So the new temperature change would be °C (8.0 °C).

For the second part of the question about the calculation of the change in enthalpy: using the formula q = mCΔT (where q is the heat energy, m is the mass of the water, C is the specific heat capacity, and ΔT is the change in temperature), and the given information (100.0 g of water with a ΔT of -13.0 °C and a C of 4.184 J/g°C), the enthalpy change (ΔH) of the reaction can be determined.

ΔH for the reaction can be calculated as q = (100.0 g)(4.184 J/g°C)(-13.0 °C) which simplifies to -5428 J or -5.428 kJ because 1 kJ = 1000 J. Since the temperature decreased, it suggests that the reaction is endothermic, absorbing heat from the surroundings.