Final answer:
The energy change when the temperature of 100.0 mL of water decreases by 4.5°C is -1892 J. The mass of NH4Cl needed to absorb the same amount of energy when dissolved in water is 119.86 g.
Step-by-step explanation:
To calculate the energy change when the temperature of 100.0 mL of liquid water decreases by 4.50∘C, we need to use the equation q = m * c * ΔT, where q is the energy change, m is the mass of the water, c is the specific heat capacity of water, and ΔT is the change in temperature.
The specific heat capacity of water is approximately 4.184 J/g°C. The mass of water can be calculated using its density, which is 1.00 g/mL. So, the mass of 100.0 mL of water is 100.0 g.
Plugging the values into the equation, we get q = (100.0 g) * (4.184 J/g°C) * (-4.50°C) = -1892 J. Therefore, the energy change when the temperature of 100.0 mL of liquid water decreases by 4.50∘C is -1892 J
To calculate the mass of NH4Cl needed to absorb the same amount of energy when dissolved in water, we can use the equation q = ΔH * n, where q is the energy change, ΔH is the enthalpy change of NH4HCl when dissolved in water, and n is the number of moles of NH4Cl.
Rearranging the equation to solve for n, we have n = q / ΔH. Plugging in the values from the question, we have n = -1892 J / 844.39 J/mol = -2.24 mol.
Since the number of moles cannot be negative, the absolute value of the number of moles is 2.24 mol.
The molar mass of NH4Cl is 53.49 g/mol. So, the mass of NH4Cl needed to absorb the same amount of energy when dissolved in water is (2.24 mol) * (53.49 g/mol) = 119.86 g.