Energy Changes Flashcards
Define exothermic/endothermic change
A change in which heat is lost to/gained from surroundings
In neutralisation reaction, when is maximum/minimum temperature reached
Maximum temperature is reached when all the reactants have reacted. Temperature returns to be the same as room temperature after cooling for a period of time
Name five physical processes which are exothermic
Freezing, condensation, deposition, crystallisation, dilution of acids and alkalis
Name five physical processes of endothermic change
Melting, evaporation, boiling, sublimation, dissolving of some ionic compounds like NH4Cl
Name 4 exothermic chemical reactions
Combustion of fuels, neutralisation reaction, reactions of acids with metals, respiration
Name 2 endothermic chemical reactions
Thermal decomposition of compounds, photosynthesis
State difference in energy level between products and reactants for exothermic reactions
Products have lower energy than reactants, difference between energy levels is equal to energy released to the surroundings during the reaction. Enthalpy change is negative
State difference in energy level between products and reactants for endothermic reactions
Products have higher energy than reactants, difference between energy levels is equal to energy absorbed to the surroundings during the reaction. Enthalpy change is positive
Describe bond breaking and bond forming in chemical reaction
Reacting particles must collide with each other. Bonds between reactants must be broken and new bonds between atoms have to form, which leads to formation of products
Define enthalpy change
The overall heat change in a reaction
Explain why the enthalpy change in exothermic reaction is negative value
Energy released during bond forming in products is more than energy absorbed during bond breaking in reactants
Explain why the enthalpy change in endothermic reaction is positive value
Energy released during bond forming in products is less than energy absorbed during bond breaking in reactants
Define bond energy
The energy absorbed to break one mole of covalent bonds. (measured in kJ/mol)
Define activation energy
Activation energy is the minimum amount of energy that reacting particles must possess in order for a chemical reaction to occur
Why wont products be formed if particles possess little energy
If reacting particles possess energy less than activation energy required, bonds in reactants will not be broken upon collision
