Chem 132 Experiment 10
Determine the enthalpy of reaction 100 mL of 2.00 M HCl 100 mL of 2.18 M NaOH Initial temp: 23.02 C Final Temp: 30.50 C Density of solution: 1.00 g/mL
-32.34 kJ/mol
How do you calculate the heat capacity of a calorimeter
1. calculate ∆T for hot and cold water [T(final)-T(hot)] [T(final)-T(cold)] 2. Calculate heat lost from hot water and gained by cold water [g of water x c of water x temperature change] 3. Calculate heat gained by calorimeter q(cal)= -[q(hot) + q(cold)] 4. Calculate the heat capacity of the calorimeter [heat gained/∆T(cold water)
T(hot): 50mL, 41.20 C T (cold): 50 mL, 21.60 C T(final): 30.80 C Calculate the heat capacity of the calorimeter
28 J/C
Procedure Part B: Neutralization of HCl and NaOH (reasoning)
Add 50 mL of HCl to 50 mL of NaOH Construct a temperature curve and determine change in temperature This is done because the temperature change is used to calculate ∆H
Procedure Part C: Heat of Neutralization of HC2H3O2 and NaOH
Add 50 mL of HCl to 50 mL of NaOH Construct a temperature curve and determine change in temperature This is done because the temperature change is used to calculate ∆H
Procedure: Part A (reasoning)
Add 50mL of hot water to 50mL of room temperature water and measure the change in temperature Construct a temperature curve and determine change in temperature This is done to measure the specific heat capacity of the calorimeter so q can be calculated
What is the instrument used in this experiment, and how can heat of the reaction be calculated
Calorimeter: instrument to measure ∆H and our specific heat capacity c. q=mc∆T q = heat energy gained or lost m= mass of water C= specific heat capacity ∆T: temperature change (Tfinal -Tinitial)
What is the definition of ∆H and how does it relate to exothermic and endothermic reactions
Enthalpy of reaction (Δ H), or heat flow, is defined as the amount of heat that would have to enter, or leave, a system in order to bring the temperature back to its initial value. Therefore (Δ H) is positive for an endothermic reaction because the heat would have to enter the system to bring the temperature back to the original value.
How do you find the enthalpy of reaction
Find temperature change of solution Calculate heat gained by solution Using the temperature change and the heat gained by the calorimeter, add value to heat gained by solution Heat of solution= -Heat of reaction Find limiting reactant of reaction and divide heat of reaction by number of moles of water produced
Why should you not heat the water to boiling in part A
Loss of water via steam could skew the results
How do the heats of reaction for the reaction of NaOH with a strong acid vs a weak acid compare
More energy would be given off (more negative value) as there would be more heat with a strong acid and base reaction as both would dissociate completely Less energy would be given off (less negative value) as less heat is given off as weak acids to not fully dissociate
What reaction is used in this experiment with the calorimeter
Neutralization reaction between an acid and base
If the the temperature probe read 1.0 C lower what would be the effect on enthalpy
No effect as the difference between initial and final readings would still be the same, just 1 degree lower
Why must you wash the probe before placing it in the HCl cup after measuring the NaOH
Residue could react and make the initial temperature appear higher
Consider the following statements about Enthalpy and identify each as True (T) or False (F). Enthalpy... Is dependent only on changes in a system between initial and final states. T/F? Is the amount of heat that must exit a system to return to starting temperature in an endothermic reaction. T/F? Is calculated as the heat of reaction as a function of the #moles of limiting reagent which reacted. T/F
T F T
What is calorimetry and what are its units
Used to measure thermal energy changes in chemical reactions Joule (J) or 1 kgm^2/s^2
How is heat of solution related to heat of reaction
heat of reaction is negative heat of solution
How is heat of neutralization defined and calculated (∆H)
∆H is defined as the enthalpy change when equal amounts of acid and base are mixed to form one mole of water ∆H=q/n (n is number of moles)
what does ∆H represent, and what do negative and positive values mean
∆H: change in enthalpy = heat of a reaction ∆H < 0 exothermic: reaction releases heat ∆H > 0 endothermic: reaction absorbs heat
