AQA · Chemistry · 8462
GCSE Chemistry: The energy change of reactions
Energy changes · AQA GCSE Chemistry (8462), specification point 4.5.1.3. Cards are generated from the exam board's own specification for "The energy change of reactions", and every card links back to the page it came from. Higher tier only. Specification © AQA — used with attribution.
10 flashcards · Free to study · No account needed
Study this deck
Preparing your cards…
All questions and answers
Read through the full deck, or practise recalling each answer above.
During a chemical reaction, is energy supplied or released when bonds in the reactants are broken?
Show answer
Energy must be supplied — bond breaking is endothermic.
During a chemical reaction, is energy supplied or released when new bonds form in the products?
Show answer
Energy is released — bond forming is exothermic.
The energy needed to break bonds and the energy released when bonds form can be calculated from ?.
Show answer
bond energies
How is the overall energy change of a reaction calculated from bond energies?
Show answer
Sum of energy needed to break bonds in the reactants minus the sum of energy released when bonds form in the products.
In an exothermic reaction, which is greater: energy released forming bonds or energy needed to break bonds?
Show answer
Energy released from forming new bonds is greater than the energy needed to break existing bonds.
In an endothermic reaction, which is greater: energy needed to break bonds or energy released forming bonds?
Show answer
Energy needed to break existing bonds is greater than the energy released from forming new bonds.
A reaction where more energy is released forming bonds than is needed to break bonds is ?.
Show answer
exothermic
A reaction where more energy is needed to break bonds than is released forming bonds is ?.
Show answer
endothermic
What sign does the overall energy change (bonds broken − bonds formed) have for an exothermic reaction?
Show answer
Negative — more energy is released forming bonds than absorbed breaking them, so the calculation gives a negative value.
Why does bond breaking require an input of energy?
Show answer
Bonds are attractive forces holding atoms together; energy must be supplied to pull the atoms apart.
Want to create your own cards? Create a free account. AI generation uses credits.