Introduction to Thermodynamics and Spontaneous Reactions

These flashcards cover key concepts from the lecture on thermodynamics, spontaneous reactions, metabolism, and the role of energy in biochemical processes.

What is the first law of thermodynamics?

Energy is neither created nor destroyed, only transferred or transformed.

What characterizes a spontaneous reaction?

A spontaneous reaction occurs without the need for external energy input; it releases energy.

How do plants contribute to energy for the body?

Plants convert light energy from the sun into chemical energy through photosynthesis, producing organic material like sugar.

What is entropy?

A measure of disorder in a system, which tends to increase in spontaneous reactions.

What are the main variables in the free energy change equation for spontaneous reactions?

Delta G (free energy), Delta H (enthalpy), and Delta S (entropy).

When is a reaction considered exergonic?

A reaction is exergonic when it releases energy, indicated by a negative Delta G.

What is the significance of Delta S in spontaneous reactions?

A positive Delta S indicates increasing disorder, making the reaction more favorable.

What happens to glucose when it is left exposed to oxygen?

Glucose will spontaneously break down into carbon dioxide and water, releasing energy.

What defines a catabolic reaction?

A catabolic reaction is a process that breaks down larger molecules into smaller ones, releasing energy.

What is metabolism?

The totality of chemical reactions in an organism, encompassing both anabolic and catabolic pathways.

What is the role of ATP in metabolic reactions?

ATP provides the energy necessary for various biochemical reactions by releasing energy when hydrolyzed.

What does it mean for a reaction to be endothermic?

An endothermic reaction absorbs heat from the surroundings.

How are spontaneous reactions assessed in terms of Delta H and Delta S?

For a reaction to be spontaneous, Delta H must be negative (releasing heat) and Delta S must be positive (increasing disorder).

What is the connection between the citric acid cycle and the electron transport chain?

The citric acid cycle produces electron carriers that are used in the electron transport chain to generate ATP.

What does the Second Law of Thermodynamics state about entropy?

It states that the total entropy (\DeltaS), or disorder, of an isolated system tends to increase over time.

How does a positive change in entropy (\DeltaS > 0) influence reaction spontaneity?

A positive change in entropy (increasing disorder) generally makes a reaction more spontaneous.

What is enthalpy (\DeltaH)?

It is a measure of the heat content of a system.

What characterizes an exothermic reaction, and how does it affect spontaneity?

An exothermic reaction releases heat (\DeltaH < 0), which makes it favorable for spontaneity.

What describes an endothermic reaction in terms of heat and spontaneity?

An endothermic reaction absorbs heat (\DeltaH > 0). It is generally not favorable for spontaneity unless compensated by a significant increase in entropy.

How does the sign of Free Energy Change (\DeltaG) determine a reaction's spontaneity?

If \Delta G < 0, the reaction is spontaneous and exergonic (releases energy). If \Delta G > 0, the reaction is non-spontaneous and endergonic (requires energy input).

What is the mathematical relationship for Free Energy Change (\DeltaG), and what does 'T' represent in the equation?

(ΔG=ΔH−TΔSΔG=ΔH−TΔS). 'T' represents the absolute temperature in Kelvin, influencing the contribution of entropy to spontaneity.

According to the Free Energy Change equation (\Delta G = \Delta H - T\Delta S), what combination of enthalpy (\DeltaH) and entropy (\DeltaS) always leads to a spontaneous reaction?

A negative \Delta H (exothermic) combined with a positive \Delta S (increasing disorder) will always result in a negative \Delta G, making the reaction spontaneous.

On an energy diagram, what indicates a spontaneous reaction versus a non-spontaneous reaction?

A reaction 'going downhill' (products have lower energy than reactants) represents a spontaneous reaction, while 'going uphill' (products have higher energy than reactants) represents a non-spontaneous reaction requiring energy input.

Provide an example of a biological non-spontaneous reaction.

The formation of sucrose from glucose and fructose is a non-spontaneous reaction that requires an input of energy.

What are coupled reactions in biological systems?

Use of the energy released from a spontaneous reaction (like ATP breakdown) to drive a non-spontaneous reaction.

What defines an anabolic reaction?

An anabolic reaction is a process that builds larger molecules from smaller ones, requiring an input of energy.

What are the four main stages of catabolism?

1. Digestion 2. Acetyl CoA production 3. Citric Acid Cycle 4. ATP production (via Electron Transport Chain)

How does an increase in temperature affect the spontaneity of a reaction with a positive \Delta S?

For reactions with a positive \Delta S (increasing disorder), raising the temperature 'T' makes the -T\Delta S term more negative, thus making the overall \Delta G more negative and increasing the likelihood of spontaneity.

When does the spontaneity of a reaction (\Delta G) become dependent on temperature 'T'?

Spontaneity becomes temperature-dependent when \Delta H and \Delta S have the same sign. If both are positive (\Delta H > 0, \Delta S > 0), the reaction is spontaneous at high temperatures. If both are negative (\Delta H < 0, \Delta S < 0), it is spontaneous at low temperatures.