Week 2 - Thermodynamics

Question 1

What is a redox (reduction-oxidation) reaction?

Answer 1

A redox reaction is a chemical reaction that involves a change in the oxidation state of elements due to the transfer of electrons. It includes oxidation (loss of electrons) and reduction (gain of electrons).

Electrons are transferred from the oxidised atom to a neighbouring atom with a greater attraction (electronegativity) for those valence electrons.

Oxidation is the loss of electrons by an atom, increasing its oxidation state.

Reduction is the gain of electrons by an atom, decreasing its oxidation state.

(OIL RIG – Oxidation Is Loss, Reduction Is Gain)

They are crucial for aquifer and soil dynamics, photosynthesis, and the degradation of toxic organic compounds.

Example: Iron loses an electron, changing from ferrous (Fe²⁺) to ferric (Fe³⁺) state.

Question 2

What is the first law of thermodynamics?

Answer 2

The First Law states that energy cannot be created or destroyed, only transferred or transformed from one form to another.
This means the total energy in a closed system is conserved.

Question 3

What is the Second Law of Thermodynamics?

Answer 3

The Second Law states that the entropy (randomness or disorder) of any isolated system will always increase over time.
In other words, systems naturally move toward a state of greater disorder — unless energy is added to maintain or increase order.

Equation:
ΔS= dq/dT
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Where:
ΔS = change in entropy (in joules per kelvin, J/K)
dq = heat added to the system reversibly
dT = absolute temperature (in kelvin, K)

What it means:
-Entropy increases when heat is added to a system at a given temperature
-The higher the temperature, the smaller the increase in entropy from the same amount of heat

Question 4

What is enthalpy in thermodynamics?

Answer 4

Enthalpy (H) is the total heat content of a system at constant pressure.
It includes the system’s internal energy and the energy required to make space for it by displacing the environment (i.e., pressure–volume work).

Think of it as the system’s “stored heat energy” when pressure is constant.

Question 5

What does ΔH (enthalpy) represent in a chemical reaction?

Answer 5

ΔH is the change in enthalpy during a reaction — it tells us how much heat is absorbed or released at constant pressure during changes of state

If ΔH is positive → Endothermic (heat gained/absorbed)
If ΔH is negative → Exothermic (heat lost/released)

Question 6

What is the standard enthalpy change (ΔH°) of a reaction?

Answer 6

It is the enthalpy change when a reaction occurs with reactants and products in their standard states (usually at 1 atm and 298 K).

Summing the enthalpies of formation (ΔHf°) (KJ) of all products and reactants, then subtracting total reactants from total products.
This is the energy needed to form them from their basic elements under standard conditions
This is multiplied by the no. of moles in the reaction.

ΔHreaction = Sum of ΔHf products − Sum of ΔHf reactants
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