Zinc dissolves in acid according to the balanced reaction:
Zn(s) + 2H^+(aq) -> Zn^2+(aq) + H2(g)
A sample of zinc is placed in the ice calorimeter. If 0.0657g of zinc causes a decrease of 0.109mL in the ice/water volume of the calorimeter, what is the enthalpy change, per mole of zinc, for the above reaction per mole of zinc.
Extra info:
Given that the enthalpy change for the process H2O(s) -> H2O(l) is +6.01 kJ/mol or 333 J/g, it can be determined that 3.68 kJ are released per mL change in the volume of the ice/water mixture.
This is what I have so far..
N(zinc)= m(zinc)/M(zinc) = 0.001 mol Zn
q(calorimeter)= -3.68 kJ/mL x 0.109mL
= -0.401 kJ
-q(rxn) = q(calorimeter)
q(rxn)= 0.401 kJ
(delta)H = 0.401 kJ/0.001 mol
= 401 kJ/mol
The answer is right, it's just that I do not understand why we would use 3.68 kJ/mL and multiply it with 0.109 mL?
Please help, much appreciated. Thank you!
3.68kj of energy are released per ml so it is actually 3.68kj/ml you need to cancel out the ml by multiplying to get the heat lost by ice water for this specific amount of ice water
Thanks!
Because we need to Cancel the mL and keep kj our main unit and the heat is released as a form of energy which is measured in Kj so basically u are multiplying these 2 numbers just for the sake of getting a pure q(calorimeter) in its energy form i.e Kj because ML is not an energy unit its used to measure volume and when u use volume ml is not used often it is mostly converted into Liters (L). I wish this helped!
To understand why we use 3.68 kJ/mL and multiply it by 0.109 mL, we need to examine the information provided and the concept of enthalpy change.
The given information states that when there is a volume change in the ice/water mixture by 1 mL, an enthalpy change of 3.68 kJ occurs. This is derived from the enthalpy change for the transition of H2O from solid to liquid, which is given as 6.01 kJ/mol or 333 J/g. Since the density of water is approximately 1 g/mL, we can calculate the enthalpy change per mL by dividing 333 J/g by the density of water (1 g/mL), which gives us 333 J/mL or 0.333 kJ/mL.
However, this enthalpy change is specific to the process of water transitioning from solid to liquid. In the given problem, we are dealing with the dissolution of zinc in an acid, not the phase change of water. Therefore, we need to consider the specific enthalpy change for this reaction.
In the problem, the decrease in volume of the ice/water mixture is given as 0.109 mL. According to the given information, for every 1 mL change in volume, there is an enthalpy change of 3.68 kJ. Hence, to determine the total enthalpy change for the reaction, we need to multiply the enthalpy change per mL (3.68 kJ/mL) by the volume change (0.109 mL):
3.68 kJ/mL × 0.109 mL = 0.401 kJ
So, the enthalpy change of the reaction is calculated as -0.401 kJ.
It is important to note that the negative sign indicates that the reaction is exothermic, as heat is released. To calculate the enthalpy change per mole of zinc, we divide the enthalpy change (-0.401 kJ) by the number of moles of zinc (0.001 mol):
-0.401 kJ / 0.001 mol = -401 kJ/mol
Hence, the enthalpy change per mole of zinc for the given reaction is -401 kJ/mol.