Help with Heat of Neutralization Homework

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Discussion Overview

The discussion revolves around a homework problem related to the heat of neutralization from a lab experiment involving the reaction of hydrochloric acid (HCl) and sodium hydroxide (NaOH). Participants are exploring the calculations for heat released during the reaction and the enthalpy change per mole of water formed, as well as clarifying concepts related to the experiment.

Discussion Character

  • Homework-related
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant calculated the heat absorbed by water (q_water) as 1465.1 J based on a temperature increase of 7°C and assumed 50 g of water.
  • The same participant expressed confusion regarding the calculation of ΔH_neutralization per mole of water formed, noting a discrepancy with expected values found online.
  • Another participant pointed out that the initial assumption of producing 50 g of water was incorrect and inquired about the concentrations of the NaOH and HCl solutions used.
  • A further response clarified that ΔH = -58 kJ/mol refers to the heat released when one mole of H+ reacts with one mole of OH- to form one mole of water, emphasizing the need to calculate the actual moles of water formed in the reaction.
  • Participants discussed the importance of understanding the stoichiometry of the neutralization reaction to accurately determine the enthalpy change.

Areas of Agreement / Disagreement

Participants generally agree on the need to clarify the number of moles of water formed in the reaction and the importance of solution concentrations. However, there is no consensus on the calculations or the interpretation of the results, as confusion remains regarding the enthalpy change per mole of water.

Contextual Notes

The discussion highlights limitations in the initial assumptions regarding the amount of water produced and the need for additional information about the concentrations of the reactants to accurately determine the enthalpy change.

Who May Find This Useful

Students studying thermochemistry, particularly those working on heat of neutralization problems in laboratory settings, may find this discussion relevant.

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Homework Statement


Im confused about this and need help
We did heat of nuetralization lab where we reacted 25mL of HCL and 25mL of NaOH using calorimeter.
The temp difference was an increase of exactly 7degC
One question asks me to show q_water (J) and to assume 50g water for the calculation
so i plugged in 50g * 4.186J/gdegC * 7degC = 1465.1J

Next it asks me what delta H_nuetralization (J) is and I wrote:
delta H_neut = q_rxn = -q_water = -1465.1J

Next it asks me for net ionic. I wrote
H^(aq) + + OH^-(aq) --> H2O(l)

Then it asks me for delta H_neut (kJ/mol), per mole of water formed and this is where I am confused, because internet search shows value should be about -58kJ/mol

50g water = 2.78mol
so if 50g water produces -1465.1J, then 1 mol water would produce 1465.1J / 2.775mol =527.0J
= 0.527kJmol - this is way off so I must be doing something wrong somewhere.
thanks for any help

Homework Equations

The Attempt at a Solution

 
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You didn't produce 50 g of water.

Were you given concentrations of NaOH and HCl?
 
Yes the whole experiement was nuetralization reaction. I had 25.0mL of NaOH and 25.0mL of HCl. I understand that the acid and base nuetralize each other and this is exothermic so heat given off but I am still confused about the whole concept for the enthalpy. thanks for any more help
 
ΔH = -58 kJ/mol means that 58 kJ of heat are released when 1 mole of H+ reacts with 1 mole of OH- to give 1 mole of water. This is what the question means when it asks for ΔH per mole of water formed - not the water initially present in the solutions. You need to work out the number of moles of water formed in the neutralization reaction, and divide 1465.1 J by that number. For that, you need the concentrations of the solutions, which Borek asked you for but you didn't give.
 

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