Energy changes Flashcards
What is enthalpy change (∆H)?
Enthalpy Change (∆H): The heat change that occurs during a chemical or physical process at constant pressure. It can be either positive (endothermic) or negative (exothermic).
What is an endothermic reaction?
Endothermic Reaction: A reaction that absorbs heat from the surroundings, resulting in a positive enthalpy change (∆H > 0). Examples include the dissolution of ammonium chloride (NH₄Cl) in water.
What is an exothermic reaction?
Exothermic Reaction: A reaction that releases heat to the surroundings, resulting in a negative enthalpy change (∆H < 0). Examples include the combustion of methane (CH₄) and the reaction of sodium (Na) with water.
What is entropy (S)?
Entropy (S): A measure of the degree of disorder or randomness in a system. A higher entropy indicates a more disordered system.
What is Gibbs free energy (∆G)?
Gibbs Free Energy (∆G): A thermodynamic quantity that indicates the spontaneity of a process. It combines enthalpy (∆H) and entropy (∆S) into a single value: ∆G = ∆H - T∆S.
What determines whether a reaction is spontaneous?
Spontaneity Criteria: A reaction is spontaneous if the Gibbs free energy (∆G) is less than zero (∆G < 0). If ∆G > 0, the reaction is non-spontaneous.
What does ∆G = 0 indicate?
∆G = 0: This indicates that the reaction is at equilibrium, with no net change in the concentrations of reactants and products.
How are ∆H, ∆S, and ∆G related?
Relationship: The relationship between enthalpy, entropy, and Gibbs free energy is given by the formula: ∆G = ∆H - T∆S, where T is the absolute temperature in Kelvin (K).
What is the significance of entropy in mixing gases?
Entropy in Mixing Gases: When gases mix, the entropy increases due to the increased disorder or randomness in the system.
What is the role of entropy in the dissolution of salts?
Entropy in Dissolution of Salts: The dissolution of salts typically increases entropy as the orderly crystal lattice breaks down into individual ions dispersed in solution.
What is an example of an exothermic reaction?
The reaction between sodium (Na) and water (H₂O) to form sodium hydroxide (NaOH) and hydrogen gas (H₂) is exothermic, releasing heat.
What is an example of an endothermic reaction?
Example: The dissolution of ammonium chloride (NH₄Cl) in water is endothermic, absorbing heat and resulting in a cooling effect.
How do you calculate the spontaneity of a reaction?
Calculation: To determine if a reaction is spontaneous, use the formula ∆G = ∆H - T∆S. If ∆G < 0, the reaction is spontaneous.
What is the graphical representation of heat changes in a reaction?
Graphical Representation: Heat changes in a reaction are often represented by enthalpy diagrams, where the y-axis represents enthalpy (H) and the x-axis represents the progress of the reaction. Exothermic reactions show a downward slope, while endothermic reactions show an upward slope.
What is the driving force for chemical reactions?
Driving Force: The driving forces for chemical reactions are the changes in enthalpy (∆H), entropy (∆S), and the temperature (T), which together determine the Gibbs free energy (∆G).
