Chemical Energetics Flashcards
(20 cards)
Category: Demonstration of Exothermic Reaction
Describe an exothermic reaction in terms of change in temperature for both the solution and the surrounding environment.
During the reaction, the temperature of the solution has decreased. Temperature of the surrounding environment, however, has increased.
Category: Demonstration of Exothermic Reaction
Explain exothermic reaction in terms of transfer of thermal energy/energy in the thermal store.
During the reaction, energy is transferred from the thermal store of the reacting particle to the thermal store of the surroundings (e.g water). The resulting solution is thus at a lower temperature than the surrounding air.
This is due to energy being transferred to the surrounding air.
Category: Demonstration of Endothermic Reaction
Explain endothermic reaction in terms of change in temperature. How does the temperature of the solution and the surroundings change respectively?
During the reaction, temperature of the mixture has increased, whilst the temperature of the surrounding air has decreased.
Category: Demonstration of Endothermic Reaction
Explain endothermic reaction in terms of transfer of thermal energy. Is thermal energy transferred from the solution to the surroundings, or vice versa?
During the reaction, energy is transferred from the surroundings to the reacting particles. The resulting particles are thus at a higher temperature than the surroundings, and thermal energy is transferred from the surrounding air.
Category: Exothermic Processes
What effect does the exothermic process have on the surroundings?
An exothermic reaction releases heat to the surroundings, and causes the temperature of the surroundings to increase.
Category: Exothermic Processes
Explain exothermic reaction in terms of bond breaking and bond forming.
Less energy is absorbed during bond breaking (where energy is absorbed to overcome the intermolecular forces of attraction between the molecules) than the energy released during bond forming. Hence, the net energy change would be a decrease in energy as more energy is released than absorbed.
Category: Exothermic Processes
Explain Exothermic Reactions in terms of enthalpy change.
For exothermic reaction, enthalpy change is negative, as energy is released to the surroundings.
Category: Endothermic Processes
Explain Endothermic Processes in terms of the effect such a reaction has on the surroundings.
Endothermic Reactions absorb heat from the surroundings, and causes the temperature of the surroundings to decrease.
Category: Endothermic Processes
Explain Endothermic reactions in terms of bond breaking and bond forming.
More energy is absorbed during bond breaking than energy is released during bond forming. Thus, the net energy change is the increase in energy.
Category: Endothermic Processes
Explain endothermic reactions in terms of enthalpy change.
The enthalpy change of endothermic reactions is positive.
Category: Explanation for Energy Change during a chemical reaction
When is energy absorbed or released?
Energy is absorbed when breaking bonds, as more energy is required to overcome the intermolecular forces of attraction between molecules.
Energy is released when forming bonds.
Category: Examples
What are some common examples of exothermic reactions?
Combustion of fuels, respiration, Neutralisation of acids with bases, reactions with acids and water, condensation and freezing processes.
Category: Examples
What are some examples of endothermic reactions?
Thermal Decomposition, Photosynthesis, Melting, Boiling, Vaporisation, Evaporation and Sublimation Processes.
Category: Enthalpy Change
Compare the differences between energy change and enthalpy change.
Energy Change refers to the energy released/absorbed when any amount of reactant is added.
Enthalpy Change refers to the energy released/absorbed during a reaction according to moles of reactants used and products formed in the equation (per mole of equation)
Category: Energy Profile and Energy Level Diagrams
What is activation energy?
In most reactions, whether exothermic or endothermic, bonds in reactant particles must first be broken/weakened before new bonds in product particles can be made.
The minimum energy required to be possessed by the reacting particles before the reaction can occur is known as the activation energy.
Category: Energy Profile and Energy Level DIagrams
How to draw the energy profile and energy level diagrams for an exothermic reaction?
The energy level of the reactants should be higher than that of the products, and thus this means that enthalpy change should be negative. For energy profile diagrams, the graph should curve upwards before descending. This distance between the maximum point of thep curve and the energy level of the reactants represent the activation energy required for the reaction to occur.
Category: Energy Profile and Energy Level DIagrams
How to draw the energy profile and energy level diagrams for an endothermic reaction?
The energy level of the reactants should be lower than that of the products, given that energy has been absorbed from the surroundings.
For energy profile diagrams, the curve ascends upwards before descending to a level which is higher than the energy level of the reactants. This means that enthalpy change is positive.
Category: Energy Profile and Energy Level DIagrams
What are the things to take note of when drawing energy profile diagrams?
1) Label x-axis as “progress of reaction”
2) Label y-axis as “energy”
3) Label the reactants and products (include formula names if given in question)
4) Label Activation Energy with a single headed arrow.
5) Label enthalpy change (include value if given, otherwise indicate if it is positive or negative, use single-headed arrow from reactants to products)
Category: Energy Profile and Energy Level DIagrams
What are the things to note when drawing energy level diagrams?
1) Do not include x-axis
2) Do not draw activation energy
3) Label reactants and products (include formula names if given)
4) Label enthalpy change (include value if given, otherwise indicate if it is positive or negative. Draw a single-headed arrow from the reactants to the products. )
Category: Enthalpy Change
When are the positive and negative signs used?
Positive sign is used for bond breaking as energy is taken in.
Negative sign is used for bond forming as energy is released.
