LECTURE 2 (Thermodynamics) Flashcards
What is an indication that a chemical reaction has taken place?
New properties become visible
What does the Law of conservation of mass state?
Matter is neither created nor destroyed in chemical reactions
What happens in Combination reactions?
Two or more elements or compounds bond to form one product
What happens in Decomposition reactions?
A reactant splits into two or more simpler products
What happens in Replacement reactions?
Elements in a compound are replaced by other elements
What happens in Combustion reactions?
A carbon-containing compound burns in oxygen from the air to produce carbon dioxide (CO2), water (H2O) and energy in the form of heat or a flame
What happens in Oxidation-Reduction reactions?
Electrons are transferred from one substance to another. If one substance loses electrons, another substance must gain electrons. Oxidation is defines as the loss of electrons, Reduction is the gain of electrons.
Describe a Reducing agent
- Loses one or more electrons
- Causes reduction
- Undergoes oxidation
- Becomes more positive (or less -ve)
Describe a Oxidising agent
- Gains one or more electrons
- Causes oxidation
- Undergoes reduction
- Becomes more negative (less +ve)
What is Kinetic energy?
Energy of motion
What is Potential energy?
Stored energy
What is the difference between an Endothermic and Exothermic reaction?
Endothermic = Absorbs heat (∆H is positive)
Exothermic = Releases heat (∆H is negative)
What is the Heat of reaction (Enthalpy change)?
Energy of bonds formed in products minus energy of bonds broken in reactants
[The difference between the energy absorbed in breaking bonds and the energy released in forming bonds]
What is a spontaneous process?
A process that once started proceeds on its own without any external influence
[Events that lead to lower energy tend to occur spontaneously]
What is Entropy?
A measure of the amount of molecular disorder in a system
What value determines spontaneity?
The value of free-energy ∆G change
How do you calculate free energy ∆G change?
∆G = ∆H - T∆S
∆G = Free-energy change
∆H = Enthalpy change
T = temperature
∆S = Entropy change
How can you tell a reaction is spontaneous or non-spontaneous?
SPONTANEOUS:
- ∆G is negative
- Free energy is released
- Process is exergonic
NON-SPONTANEOUS:
- ∆G is positive
- Free energy is added
- Process is endergonic
What is the difference between exergonic and endergonic?
EXERGONIC = the products are at a lower energy level than the reactants
ENDERGONIC = products are higher than reactants
What is important to remember about ∆G?
Just because a chemical reaction has a favourable free-energy change does not mean it occurs rapidly -> Value of ∆G tells us only if it can occur not how fast it will take place or details about the molecular changes
What does increase in temperature do?
Increase in temp -> Increase in frequency of collisions -> Increase in forcefulness of collisions -> Increase in reaction rate
What is a catalyst?
A substance that accelerates a chemical reaction but is itself unchanged in the process
What happens in equilibrium?
Forward and reverse reactions have stopped
