Ex2: Introduction to Calorimetry

• specific heat, s


  heat necessary to raise the temp. of one gram of a substance by 1 degree
• heat capacity / calorimeter constant, C


  amount of energy required to raise the temp. of the calorimeter by 1 degree.

  C = m x s
• enthalpy, delta H


  the total heat content of a system
• heat of reaction, q


  the heat absorbed or released during a complete chemical rxn
• calorimeter


  measures change in temp of an isolated reaction
• initial pressure = final pressure
• qrxn + qsol = 0
• Delta H = q = mass x s x delta T OR Delta H = q = C x delta T
• Under what experimental conditions is the heat of reaction, q, equal the enthalpy change?

  At constant pressure
• The dissolution of NaOH is an exothermic reaction
• How do you calculate the Heat of Dissolution of NaOH? (the heat of solution)

  Step 1:

  calculate moles of NaOH

  n = m/M

  Step 2:

  calculate the heat of solution for NaOH per mole of NaOH (molar enthalpy) assuming NO heat lost to calorimeter

  Delta H sol. = -qrxn/n

  Step 3:

  calculate the heat of solution for NaOH per mole of NaOH including heat lost to calorimeter

  qrxn = -qcal - qsol

  (qsol was calculated in step 2)
• heat of solution per mole of NaOH (no heat lost) calculation


  Delta H sol. = -qrxn/n

  Delta H sol. = -(m x s)(delta T) / n
• heat of solution for NaOH per mol of NaOH including heat lost to calorimeter

  qrxn = -qcal -qsol

  qrxn = -(m x s) -qsol
• calculate calorimeter constant

  qcal = -qhot - qcold

  Ccal delta T = -(m x s x delta T)hot water - (m x s x delta T)cold water

  rearrange to solve for Ccal
• In a neutralization reaction involving a strong acid and a strong base the heat of reaction


  Is always -55.90 kJ per mol of water produced
• Assuming no heat lost to the calorimeter, calculate heat liberated from the neutralization reaction

  qneut = (msol)(ssol)(delta T)
• Calculate the moles of water formed in the reaction

  n = -q neut / -delta H neut
• including heat lost to the calorimeter, calculate heat liberated in the neutralization reaction

  qrxn = qcal - qsol
• Which type of balance will be used in the calorimetry experiment, and, how many decimals will be displayed by the balance?

  top-loading balance, 2 decimal places
• 10 g of sodium hydroxide solid is added to a calorimeter which contains 200 mL deionized water, and the temperature change is monitored for 30 minutes.For calculations involving this system, what value for mass, m, would be used?

  210 g, the mass of the resulting solution in the calorimeter
• To determine the specific heat of a a metal, the technique given in the calorimetry background material makes the assumption that heat gained by the water is equal to the heat lost by the metal. If this assumption were not made, what other value must be included in the calculation for accuracy?

  Heat capacity of the calorimeter