Module 3 Chapter 9
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What is enthalpy defined as
The total heat content within a system
What is a chemical system
All the atoms, ions, and molecules that make up all the chemicals in a region of observable space
What is enthalpy measured by
The heat absorbed from or released into the surroundings.
what does the universe consist of
The systems and surroundings
What is the law of conservation of energy
Energy is not created or destroyed. It is only transferred during the process.
What is the heat energy released by a chemical reaction equal to
It is equal to the heat energy gained by the surroundings.
What is the formula for enthalpy change
^H = H (products) - H (reactants)
Because of the conservation of energy what happens to the energy
The change in energy has to be transferred and this transfer takes place between the system and the surroundings.
What are examples of exothermic reactions
Combustion neutralisation Oxidation reactions Displacement
What is an exothermic reaction
A reaction that transfers energy to their surroundings and can be identified by an increase in the temperature of the surroundings.
What is the energy transfer in an exothermic reaction
Energy transfer from systems to surroundings
What are the enthalpies of the products and reactants relative to each other in an exothermic reaction and what is ^H
H products < H reactants ^H is negative
What is activation energy
The minimum amount of energy required for a reaction to take place
What does the enthalpy profile diagram and reaction profile diagram of an exothermic reaction look like
DRAW IT
What can an exothermic reaction be identified by
An increase in the temperature of the surroundings
What is an endothermic reaction in terms of energy and temperature
A reaction that takes in energy from its surroundings and can be identified by a decrease in the temperature of the surroundings.
What is the relative energy of the products and reactants in an endothermic reaction and what is ^H
H products > H reactants ^H is positive
What does the enthalpy profile diagram and reaction profile diagram look like for an endothermic change
DRAW IT
If the reaction conditions change what happens
The reactants and products enthalpy can change which means ^H can change as well.
What are standard conditions
Standard pressure - 100kPA Standard temperature - 298K (25 C) Standard concentration - 1mol/dm3 (only with solutions) Standard state - the physical state of a substance under standard conditions
What is the symbol for when an experiment is done at standard conditions
DRAW IT
What is 1 atmosphere in kPA
101 kPA =101,000 Pa = 1 atm
What is enthalpy change of formation
The enthalpy change when 1 mole of a compound is formed from its elements under standard conditions with all reactants and products in their standard state.
What is the enthalpy change of formation of an element always
0 KJ/mol