calorimetry - measurement of heat flow  

• calorimeter - device used to measure heat flow
• heat capacity - amount of heat needed to raise temperature by 1°C
  • molar heat capacity - heat capacity of 1 mol of a substance
• specific heat - heat capacity of 1g of a substance
  • specific heat = quantity of heat transferred / (grams of substance x temperature change)
  • = q / (m x DT)
• q = specific heat x grams of substance x DT

Find amount of heat needed to warm 250 g of water from 22°C to 98°C  

• Given:
  • specific heat of water = 4.18 J/g-K
• change in K same as change in °C
• q = specific heat of water x grams of water x DT
• = 4.18 J/g-K x 250g x 76K
• = 7.9 x 104 J

constant-pressure calorimetry - heat gained by solution same as heat lost by reaction  

• qsoln = specific heat of solution x grams of solution x DT = -qrxn

Find enthalpy change for reaction if temperature of solution in calorimeter changed from 21.0°C to 27.5°C when 50mL of 1.0M HCl was mixed with 50mL of 1.0M NaOH  

• Given:
  • total volume of solution = 100 mL
  • density of solution = 1.0g/mL
  • specific heat of solution = 4.18 J/g-K
• mass of solution = 100mL x 1.0g/mL = 100g
• temperature change = 27.5 - 21.0 = 6.5°C = 6.5K
• qrxn = -(4.18 J/g-K)(100g)(6.5K) = -2.7 x 103 J = -2.7 kJ
• 50mL x 1M = (0.050L)(1.0 mol/L) = 0.050 mol HCl or NaOH in solution
• enthalpy change per mol = -2.7 kJ / 0.050 mol = -54 kJ/mol

bomb calorimetry (constant-volume calorimetry) - studies combustion reactions  

• compound reacts w/ excess oxygen
• combustion started by electrical spark
• qrxn = -Ccal x DT
  • Ccal = heat capacity of calorimeter

Find heat of reaction for comubstion of 4.00g of CH6N2 if its combustion in a calorimeter w/ heat capacity of 7.794 kJ/ °C changes temperature from 25.00°C to 39.50°C  

• qrxn = -Ccal x DT
• DT = 39.50 - 25.00 = 14.50°C
• Ccal = 7.794 kJ/°C
• qrxn = -(7.794 kJ/°C)(14.50°C) = -113.0 kJ
• heat of reaction per mol = -113.0 kJ / 4.00g CH6N2 x 46.1g CH6N2 / 1 mol CH6N2 = -1.30 x 103 kJ/mol CH6N2

fuel value - energy released when 1g of material is combusted  

• proteins/carbohydrates produce about 17kJ/g
• fats produce 38kJ/g
• fossil fuels - formed from decomposition of plants/animals
  • natural gas - gaseous hydrocarbons
  • petroleum - liquid containing mostly hydrocarbons
  • coal - solid w/ hydrocarbons of high molecular weight; most abundant fossil fuel
  • syngas - "synthesis gas"; coal undergoes coal gasification to become mixture of methane, hydrogen, carbon dioxide gas
• nuclear energy - energy released through splitting/fusion of atom nuclei
• renewable energy - essentially inexaustible energy
  • solar energy from sun w/ solar cells (photovoltaic devices)
  • wind energy from windmills
  • geothermal energy from heat in Earth's mass
  • hydroelectric energy from flowing rivers
  • biomass energy from crops, biological waste