Question

A student conducts an experiment to determine the enthalpy of solution for lithium chloride dissolved in water. the student combines 5.00 grams of lithium chloride with 100.0 ml of distilled water. the initial temperature of the water is 23.0°c and the highest temperature after mixing reaches 33.0°c. assume a density of 1.00 g/ml and a specific heat of 4.18 j g • °c . the calorimeter constant was found to be 20.0 j

Answer 1

The enthalpy change of the solution can be calculated using the formula q = mc∆T, where q is the heat absorbed or released, m is the mass of the solution, c is the specific heat capacity of the solution, and ∆T is the change in temperature. The amount of heat involved in the dissolution of lithium chloride is 4359 J, and the reaction is exothermic.

Step-by-step explanation:

The enthalpy change of a solution can be determined using the formula q = mc∆T, where q is the heat absorbed or released, m is the mass of the solution, c is the specific heat capacity of the solution, and ∆T is the change in temperature. In this case, the initial temperature of the water is 23.0°C and the highest temperature reached after mixing is 33.0°C. The mass of the solution can be calculated by adding the mass of lithium chloride and the mass of water.

Mass of solution = mass of LiCl + mass of water = 5.00 g + 100.0 g = 105.0 g

Using the given specific heat capacity of 4.18 J/g·°C and the formula for q, we can now calculate the amount of heat involved in the dissolution of lithium chloride.

q = mc∆T

q = (105.0 g)(4.18 J/g·°C)(33.0°C - 23.0°C)

q = 4359 J

The amount of heat involved in the dissolution of lithium chloride is 4359 J. To determine if the reaction is exothermic or endothermic, we can examine the temperature change. In this case, the temperature increased, indicating an exothermic reaction.

Answer 2

I believe that this problem has 6 questions:

a) Is the reaction endothermic or exothermic? Why?
b) Calculate the temperature change of the solution in the calorimeter.
c) Calculate the total mass of the solution in the calorimeter.
d) Calculate the energy change of the solution.
e) Calculate the energy change of the calorimeter.
f) Calculate the total change of enthalpy of the solution in kJ/mole.

The answers are the following:

a) This is exothermic because the temperature of the water increased hence heat energy was released by the reaction.

b) 33 – 23 = 10C

c) 100 ml x 1 g/1 ml = 100 g

d) The formula for change in energy is:

Energy change = mass of solution x temperature change x specific heat
Energy change = 100 g x 10C x 4.18 Joules/gC = 4,180 Joules

e) 20 Joules/C x 10C = 200 Joules

f) First calculate for moles of LiCl: 5.00 g LiCl x 1 mole LiCl/42.4 g = 0.118 moles
So the total energy given off = 4,180 J + 200 Joules = 4,380 Joules
Enthalpy change, delta H is -4,380
-4380 Joules/0.118 moles = -37,119 Joules/mole
-37,119 Joules/ 1mole x 1 kilojoule/1000 Joules = -37.1 kilojoules
ΔH = -37.1 kJ/mole