The lab we are doing is: Determining the ENTHALPY of a Chemical Reaction.
There are three reactions. Reaction 1: NaOH + HCl, Reaction 2: NaOH + NH4Cl, and Reaction 3: HCl + NH3.
I found the max temp, initial temp, and temp change of each reaction. Can you help me with Reaction 1. I can figure out the other two if I get help on Reaction 1.
My question is how do you find: (please show detailed steps, really appreciate it!)
1. q surroundings (J)=
2. q reaction (J)=
3. ∆H rxn (kJ) [per mole]
4. Using Hess's Law
5. Accepted Values ∆Hrxn (kJ) (per mole)
To find the values you mentioned for Reaction 1, we can follow these steps:
1. q surroundings (J):
- The heat absorbed or released by the surroundings can be calculated using the equation q surroundings = m * c * ∆T, where m is the mass of the solution and c is the specific heat capacity of the solution.
- First, determine the mass of the solution. This can be the sum of the mass of the HCl and NaOH used.
- Use the specific heat capacity of water (4.18 J/g·°C) as an approximation for the specific heat capacity of the solution.
- Calculate ∆T by subtracting the initial temperature from the maximum temperature achieved during the reaction.
- Plug in the values into the formula to calculate q surroundings.
2. q reaction (J):
- The heat absorbed or released by the reaction can be calculated using the equation q reaction = -q surroundings, as heat is exchanged between the reaction and its surroundings.
- Take the negative of the previously calculated q surroundings value.
3. ∆H rxn (kJ) [per mole]:
- Use the equation ∆H rxn = (q reaction / number of moles of limiting reactant) / 1000 to find the enthalpy change per mole of the limiting reactant.
- Identify the limiting reactant in the reaction based on the stoichiometry of the balanced equation.
- Calculate the number of moles of the limiting reactant used in the reaction.
- Divide q reaction by the number of moles of the limiting reactant and then divide by 1000 to convert from J to kJ.
4. Using Hess's Law:
- To use Hess's Law, you need to find other reactions with known enthalpy changes that, when combined, give you Reaction 1.
- Look for reactions involving the same compounds in different combinations or the reverse of Reaction 1.
- By manipulating and combining these reactions, you can cancel out certain compounds and obtain Reaction 1.
- Add together the enthalpy changes (∆H rxn) of the individual reactions to get the ∆H rxn for Reaction 1.
5. Accepted Values ∆H rxn (kJ) (per mole):
- Research or reference books may provide accepted values for ∆H rxn for specific reactions.
- Compare your calculated ∆H rxn with the accepted values to determine the level of accuracy and precision in your experiment.
Remember to record your observations, uncertainties, and sources of error throughout the experiment to ensure accurate calculations.