Energy Flow & Chemical Energy Flashcards
(8 cards)
In thermodynamic analyses, how are ‘system’ and ‘surroundings’ defined?
The system is the portion of the universe under study (e.g., reacting species); everything else constitutes the surroundings.
Classify the combustion of methane in terms of heat flow.
It is an exothermic process because heat is released from the system to the surroundings.
Provide one example of an endothermic reaction mentioned in the slide deck.
The formation of nitric oxide from nitrogen and oxygen gas is endothermic, requiring heat absorption.
What sign convention is used for q in exothermic versus endothermic reactions?
q < 0 for exothermic (heat leaves the system); q > 0 for endothermic (heat enters the system).
Relate bond strength to potential energy differences between reactants and products in an exothermic reaction.
Products possess stronger bonds and lower potential energy relative to reactants; the excess energy is liberated as heat.
Why does increasing potential energy imply weaker chemical bonds?
Because additional energy is stored in the system rather than being released through bond formation, indicating less stable (weaker) bonding interactions.
Explain the energy balance between bond breaking and bond forming in endothermic processes.
The energy required to break the reactant bonds exceeds the energy released upon product bond formation, resulting in net heat absorption.
How does the concept of enthalpy change (ΔH) capture these potential-energy differences?
ΔH equals the heat exchanged at constant pressure; its sign directly reflects whether bond-energy differences cause heat release or absorption.
