Thermo Dynamics (5/8)
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Calorimetry and how it works
It mimics combustion
How is the body doing combustion reactions?
Molecules are consumed in the presence of oxygen, producing water and carbon dioxide The body derives energy from this
Units of heat
Joules or 4.184 Cal 1 Cal = 1000 cal = 1 kcal This is easier to see rather than thousands of calories
Definition of 1 cal
Amount of energy required to raise the temperature of 1 gram of water by 1 degree C
Equation for heat
Q= mc*Change in T
Specific heat capacity (c)
energy required to raise temperature of 1 gram of substance by 1 degree C
What is Enthalpy?
Total heat in a thermodynamic system Units= [J]
Enthalpy equation
H= U + P*V = Q
Endothermic vs. Exothermic
Exothermic= losing heat and H is - Endothermic= gaining heat and H is +
Bond dissociation energy
Enthalpy change associated with breaking bonds
Rules for adding enthalpy
• Each step must be ordered in forward reaction • Reverse sign of H when reversing order of a step • Multiply by coefficients
Gibbs Free energy
Energy that can be used to perform work in a reversible reaction
Free energy state of a system
G= H - T*S
Linking equilibrium constant and gibbs free energy
If Keq > 1 then G <1 = -, spontaneous If Keq < 1 then G >1 = +, non-spontaneous
Equilibrium constant under standard condition
G= -RT*lnKeq
Catalysts
Increase rate of reaction by lowering activation energy
Relationship between Keq and Q
When Keq=Q, equilibrium When Keq > Q, products favored When Keq < Q, reactants favored