Unit 2 Topic 3 ✓ Flashcards
Physical chemistry: Thermochemistry
What is Thermochemistry
Thermochemistry is the study of the changes in energy that occur during chemical reactions
What is Thermodynamics?
Thermodynamics is the study of heat and temperature and their relation to other forms of energy and work
What is the 1st Law of Thermodynamics?
The 1st law of thermodynamics is:
‘the total energy of the universe is constant, energy can neither be created nor destroyed. It can be converted from one form to another while the total energy remains the same’
What is an Exothermic reaction
An exothermic reaction is one where energy is released to the surroundings, so temperature of surroundings will increase. The enthalpy change is negative as the system loses energy. Reactants will have a higher potential energy than products
What is an Endothermic reaction?
An endothermic reaction is one where energy is absorbed from the surroundings, so temperature of surroundings will decrease. The enthalpy change is positive as the system gains energy. Reactants will have a lower potential energy than products
What is Enthalpy? (H)
Enthalpy is a thermodynamic quantity equivalent to the total heat content of a system.
It is equal to the internal energy plus the product of pressure and volume
H cannot be measured but a change in H can (enthalpy change)
Enthalpy = (H = E + PV) - Don’t need to know
What is the Standard state of a substance?
The standard state of a substance is the most stable state of that subtance under standard conditions
Pressure = 1 atmosphere
Temperature = 298K (kelvin)
e.g. Oxgen is a gas under standard conditions
What is the Standard enthalpy of formation?
The standard enthalpy of formation is the enthalpy (H) when one mole of a substance is formed from its elements in their standard states
NOTE: The enthalpy of formation of an element is 0
What is the Standard enthalpy of a reaction?
The standard enthalpy of a reaction is the enthalpy change for a reaction in which the reactants are in their standard states at a specified temperature
NOTE: Expression for this calculation in data book
What is Entropy?
Entropy is a measure of the degree of disorder of a system.
An ordered system at low temperature has low entropy. A disordered system at high temperature has high entropy.
NOTE: Solids are more ordered than liquids etc
What is the 2nd Law of Thermodynamics?
The 2nd law of thermodynamics is:
‘the total entropy of a reaction system and its surroundings always increases for a spontaneous (feasible) process’
NOTE: If a reaction can proceed, either the reaction system or it’s surroundings will become more disordered
What is the 3rd Law of Thermodynamics?
The 3rd law of thermodynamics is:
‘ The energy of a perfect crystal at a temperature of 0 Kelvin is zero’
NOTE: If the temperature is at absolute zero (0K) then a substance cannot be any more ordered
What is a Spontaneous (feasible) reaction?
A spontaneous (feasible) reaction is a reaction that proceeds without any external input, on its own accord
What is the temperature in Celsius, equivalent to 0K? (Kelvin)
0K is equal to -273 celsius
What is Standard Entropy?
Standard entropy is the entropy of one mole of a substance in its standard state (298K and 1 atm)
What is Gibbs Free Energy?
Gibbs free energy is the energy that is available in a system to do work
NOTE: It links enthalpy and entropy
