Chp 5 Thermochemistry

5.1 Energy Basics

thermochemistry - the amount of heat absorbed or released during chemical and physical changes

Energy - the capacity to supply heat or do work

  • work - energy required to move something against a force

potential energy

energy an object has because of its relative position, composition, or condition

kinetic energy

energy that an object possesses because of its motion

kinetic energy →thermal energy - kinetic energy associated with the random motion of atoms and molecules

  • Heat (q) - transfer of thermal energy between two bodies at different temperatures

exothermic process

change that releases heat

endothermic process

change that absorbs heat

Ways of measuring energy?

  • calories (cal) - energy required to raise one gram of water by 1 degree C (1 kelvin)

    • Calorie - for food. capital C means kilocalorie

  • joule (J) - amount of energy used when a force of 1 newton moves an object 1 meter

    • 1 J = 1 kg m2/s2

    • 1 calorie =l 4.184 joules

heat capacity

equation for heat capacity

body of matter is the quantity of heat (q) it absorbs or releases when it experiences a temperature change (ΔT) of 1 degree Celsius (or equivalently, 1 kelvin)

  • extensive property

SPECIFIC heat capacity

equation for specific heat capacity

quantity of heat required to raise the temperature of 1 gram of a substance by 1 degree Celsius (or 1 kelvin)

  • intensive property

another kind of specific heat capacity

  • molar heat capacity - intensive property. heat capacity per mole of a particular substance and has units of J/mol °C

if the mass of a substance is known then:

5.2 Calorimetry

calorimetry - measure the amount of heat involved in a chemical or physical process

system - substance(s) undergoing chem or physical change

surroundings - all other matter, including measurement tools, that provide or absorb heat from the system

ideally a calorimeter only measures the heat transfer between the substances & has no energy influence from the surroundings

    qsubstanceM+qsubstanceW=0q_{substance}M+q_{substance}W=0

aka the heat gained by substance M = the heat lost by substance W

so there is the same idea when

    qreaction=−qsolutionq_{reaction}=-q_{solution}

bomb calorimeter - used to measure energy produced by reactions w lots of heat & gaseous products. (e.g. combustion reactions)

nutritional calorie (Calorie) - 1 Calorie = 1000 calories, the amount of energy need to heat 1 kg of water by 1 °C

5.3 Enthalpy

internal energy (U) / (E) - the total of all possible kinds of energy present in a substance