Thermodynamics
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What do chemical reactions take place as a result of?
bond breaking and bond making reactions
What kind of reaction is bond breaking?
endothermic
What kind of reaction is bond making?
exothermic
What is thermochemistry the study of?
the study of energy changes during chemical reactions, measured in kJ mol-1
What are energy changes measured in terms of?
enthalpy changes (or changes in energy contents)
What does a change in energy content result in?
a change in temperature of the surroundings
What do total enthalpy changes always refer to?
the system and the surroundings
What can the system be regarded as?
the part of the world we are investigating e.g. a chemical reaction
What are the surroundings regarded as?
the rest of the world e.g. the air surroundings the reaction vessel, or water the reaction is taking place in.
What is important to remember about the total amount of energy during a chemical reaction?
The total amount of energy is unchanged during a chemical reaction - energy may be exchanged between the materials and the surroundings, but the total amount of energy of the materials and surroundings remains constant
What is the first law of thermodynamics?
energy can neither be created nor destroyed, but can be changed from one form to another
State Hess’s law.
The enthalpy change for a reaction is the same regardless of the route taken
What are the standard conditions for temp and pressure?
298K (25’c) and 1 atmosphere respectively (STP)
What are substances said to be?
in their standard state, i.e. their normal physical states under standard conditions
What concentration are solutions at in their standard state?
1 mol l-1
What are enthalpy changes measured under standard conditions known as? What symbol is used?
a standard enthalpy change delta H’
What is the enthalpy of formation?
the enthalpy change when 1 mole of a substance is formed for its elements under standard conditions.
What is the standard enthalpy of formation of an element?
0
How can the standard enthalpy of a reaction being calculated?
using standard enthalpies of formation
Define entropy.
A term which refers to the chaos or disorder in a system, and measure of chaotic dispersal of energy and matter.
The greater the disorder in a system, the…
greater the entropy
Describe the effect of temperature on entropy.
Entropy increases as temperature increases
What is the standard molar entropy, S*?
the entropy content of one mole of a substance, under standard conditions
What are the units of entropy?
JK-1 mol-1