enthalpy Flashcards
What are chemical bonds?
They are the forces of attraction that bind atoms together
And chemical energy lies within these bonds, this is a form of potential energy
what is the conservation of energy?
In chemical reactions, energy is changed from one form to another :
Chemical energy-> thermal energy
No energy is lost as it is converted from one form to another
What are some factoids enthalpy?
Enthalpy (H) is the thermal energy that is stored in a system
Fun Fact: we can’t measure the direct enthalpy of profits and reactants so instead we can measure the amount of energy that is absorbed or released to the surroundings (e.g. water in the eq, Q=mc(delta)T)
This can be done by looking at the change in thermal energy.
In calorimetry what does heat gain to the surroundings mean?
Exothermic, there is heat loss in a chemical system
In calorimetry what does heat loss to the surroundings mean?
Endothermic, heat gain in the chemical system
What is enthalpy change?
Enthalpy change is the heat energy change at a constant pressure
In delta H power theta, what does theta indicate?(pimsole sign)
Standard conditions I’m either pressure (100KPa) or temperature (298K)
what are standard states?
They are the states which substances are under in standard conditions
E.g. the standard state of water is liquid and the standard state of magnesium is solid
What is a system?
[these are part of the terminology used to discuss components of chemical reactions]
A system is the atoms and bonds involved in a chemical reaction (like in the le chat principle from equilibrium)
What is the surroundings?
Everything else besides the system
what does exothermic mean?
A reaction which releases thermal energy to the surroundings as the products have less energy than the reactants.
(Nether world)
What does endothermic mean?
When thermal energy is absorbed from the surroundings into the reaction as the products have more energy than the reactants.
( Endermen)
what is the exothermic reaction profile?
- the enthalpy of the products
What is the reaction profile of endothermic reactions?
- the chemical reaction absorbs heat
- there is a heat gain from the surroundings
- the enthalpy of the products > reactants
- enthalpy change is positive
What is activation energy?
The minimum energy required to start a reaction
Why does there have to be an input of energy in exothermic reactions?
Although the products have a lower energy than the reactants, the input of energy is required to break the initial bonds to start the reaction. Once the activation energy has been overcome the energy output of the reaction provides enough energy to sustain the reaction
As a result the reaction becomes self sustaining
why does there have to be an input of energy in endothermic reactions?
The products have a higher energy than the reactants so nothing happens unless heat is added to the reaction
What is the enthalpy change of formation?
The energy change that takes the place when one mole of a compound is formed from it’s constituent elements in their standard state under standard conditions
E.g. Li(s)+1/2 F2(g)-> LiF(s)
What is the enthalpy change of combustion?
The energy change that takes place when one mole of a substance is completely combusted.
E.g. H2(g) +1/2 O2 (g) ->H2O(l)
What is the enthalpy change of neutralisation?
The energy change associated with the formation of one mole of water from a neutralisation reaction under standard conditions
E.g. HCl(aq) + NaOH (aq) -> NaCl(aq) +H2O(l)
To sum up just rebook at the chapter about reversible reactions and equilibrium
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