Chemical Energetics Flashcards
(22 cards)
What is the purpose of chemical reactions?
Chemical reactions occur so that elements can achieve a more stable energy state by gaining a full outer shell of electrons.
What is the definition of ‘system’ in the context of chemical reactions?
‘System’ refers to the reacting chemicals.
What is the definition of ‘surroundings’ in the context of chemical reactions?
‘Surroundings’ refers to anything other than the chemicals reacting.
What is transferred in exothermic reactions?
In exothermic reactions, thermal energy is transferred from the system to the surroundings.
What happens to the energy of the system in exothermic reactions?
The energy of the system decreases, resulting in a negative energy change.
What is the effect of exothermic reactions on the temperature of surroundings?
The temperature of the surroundings increases because thermal energy is released.
What are typical examples of exothermic reactions?
Typical examples include combustion, oxidation, and neutralisation.
What is a practical application of exothermic reactions?
Hand warmers used in wintertime are based on the release of heat from an exothermic reaction.
What is transferred in endothermic reactions?
In endothermic reactions, thermal energy is transferred from the surroundings to the system.
What happens to the energy of the system in endothermic reactions?
The energy of the system increases, resulting in a positive energy change.
What is the effect of endothermic reactions on the temperature of surroundings?
The temperature of the surroundings decreases because thermal energy is absorbed.
What are typical examples of endothermic reactions?
Typical examples include electrolysis, thermal decomposition, and the first stages of photosynthesis.
What is a practical application of endothermic reactions?
Cold packs for sports injuries are based on endothermic reactions, designed to take heat away from an injured area.
What happens to the energy of products in exothermic reactions?
The energy of the products will be lower than the energy of the reactants.
How is the overall energy change represented in exothermic reactions?
The overall energy change is negative and is represented on the reaction profile with a downwards-arrow.
What happens to the energy of products in endothermic reactions?
The energy of the products will be higher than the energy of the reactants.
How is the overall energy change represented in endothermic reactions?
The overall energy change is positive and is represented on the reaction profile with an upwards-arrow.
What is activation energy?
The minimum amount of energy required for a successful collision, where reactant particles are rearranged to form products.
This minimum amount of energy is called the activation energy, Ea.
How does activation energy vary among reactions?
Different reactions have different activation energies, depending on the chemical identities involved.
Reactions with higher activation energies require more energy to start than those with lower activation energies.
What is enthalpy change?
The transfer of thermal energy during a reaction, represented by ΔH.
ΔH is positive for an endothermic reaction and negative for an exothermic reaction.
What characterizes exothermic reactions?
If more energy is released than absorbed, the reaction is exothermic.
The change in energy is negative since the products have less energy than the reactants, resulting in a negative ΔH value.
What characterizes endothermic reactions?
If more energy is absorbed to break bonds than is released to form new bonds, the reaction is endothermic.
The change in energy is positive since the products have more energy than the reactants, resulting in a positive ΔH value.
