Using a coffee-cup calorimeter, it is found that when an ice cube with a mass of 24.6 g melts, 8.19 kJ of heat are absorbed.
(a) Calculate the change in enthalpy per gram and per mole of water.
(b) Write the thermochemical equation for this physical change.
(c) What mass of ice must be melted to produce 10.0 kJ of heat?
delta H = 8190 J/24.6 g
Multiply by molar mass water to convert to J/mol.
H2O(s) + heat ==> H2O(l)
I have a problem with the last question. If ice is to be melted, it must absorb heat, not produce heat. The number you want is J/g (from #1) x #grams = 10,000. Solve for #grams.
(a) To calculate the change in enthalpy per gram of water, we divide the amount of heat absorbed by the mass of the ice cube.
Change in enthalpy per gram = Heat absorbed / Mass of ice cube
Change in enthalpy per gram = 8.19 kJ / 24.6 g
Change in enthalpy per gram = 0.333 kJ/g
To calculate the change in enthalpy per mole of water, we need to convert grams to moles. The molar mass of water (H2O) is 18.015 g/mol.
Change in enthalpy per mole = Change in enthalpy per gram / Molar mass of water
Change in enthalpy per mole = 0.333 kJ/g / 18.015 g/mol
Change in enthalpy per mole = 0.0185 kJ/mol
(b) The thermochemical equation for the physical change of ice melting can be written as:
H2O(s) → H2O(l)
(c) To calculate the mass of ice that must be melted to produce 10.0 kJ of heat, we can use the equation:
Mass of ice = Heat produced / Change in enthalpy per gram
Mass of ice = 10.0 kJ / 0.333 kJ/g
Mass of ice = 30.03 g
To answer these questions, we need to use the concepts of calorimetry, enthalpy, and stoichiometry.
(a) To calculate the change in enthalpy per gram and per mole of water, we can use the given information that 8.19 kJ of heat are absorbed when a 24.6 g ice cube melts.
Change in enthalpy per gram of water = Heat absorbed / Mass of water
Change in enthalpy per gram of water = 8.19 kJ / 24.6 g
Change in enthalpy per gram of water = 0.333 kJ/g
To calculate the change in enthalpy per mole of water, we need to convert grams to moles using the molar mass of water, which is 18.015 g/mol.
Change in enthalpy per mole of water = Change in enthalpy per gram of water / Molar mass of water
Change in enthalpy per mole of water = 0.333 kJ/g / 18.015 g/mol
Change in enthalpy per mole of water ≈ 0.0185 kJ/mol
Therefore, the change in enthalpy per gram of water is 0.333 kJ/g, and per mole of water is approximately 0.0185 kJ/mol.
(b) The thermochemical equation for this physical change can be represented as:
H2O(s) → H2O(l)
This equation indicates the melting of ice, where solid water (ice) is converted to liquid water.
(c) To calculate the mass of ice that must be melted to produce 10.0 kJ of heat, we can use the given change in enthalpy per gram of water to determine the mass of water involved.
Mass of water = Heat produced / Change in enthalpy per gram of water
Mass of water = 10.0 kJ / 0.333 kJ/g
Mass of water ≈ 30.03 g
Therefore, approximately 30.03 grams of ice must be melted to produce 10.0 kJ of heat.