C3.2 Flashcards
What is an exothermic reaction?
A reaction that transfers energy to the surroundings, increasing the temperature.
Examples: Combustion, oxidation, neutralization, hand warmers.
What is an endothermic reaction?
A reaction that takes in energy from the surroundings, decreasing the temperature.
Examples: Thermal decomposition, reaction of citric acid with sodium hydrogen carbonate, sports injury packs.
How can you identify an exothermic reaction on a reaction profile?
The products have lower energy than the reactants, and the energy change arrow points downwards.
How can you identify an endothermic reaction on a reaction profile?
The products have higher energy than the reactants, and the energy change arrow points upwards.
What is activation energy?
The minimum amount of energy that particles need to collide and react.
What happens to bonds during a chemical reaction?
Breaking bonds requires energy (endothermic).
Forming bonds releases energy (exothermic).
How do reaction profiles show activation energy?
It is the energy peak that reactants must reach before forming products.
How do you calculate the overall energy change of a reaction?
Overall energy change = Energy required to break bonds − Energy released when forming bonds.
What does it mean if the energy required to break bonds is greater than the energy released forming bonds?
The reaction is endothermic.
What does it mean if the energy released when forming bonds is greater than the energy required to break bonds?
The reaction is exothermic.
Why are hand warmers exothermic?
They release heat as the chemical reaction transfers energy to the surroundings.
Why are sports injury packs endothermic?
They absorb heat from the surroundings, cooling the affected area.
How do you recognize activation energy on a reaction profile graph?
It is the energy difference between the reactants and the peak of the curve.
What are the units of energy change in reactions?
Kilojoules per mole (kJ/mol).
Why do exothermic reactions feel hot?
Heat is transferred from the reaction to the surroundings, increasing temperature.
Why do endothermic reactions feel cold?
Heat is absorbed from the surroundings, reducing the surrounding temperature.
How do you know if a reaction is reversible?
If it can go both ways, with products able to convert back to reactants under certain conditions. Represented by a double arrow (⇌).
What is a reaction profile?
A diagram that shows the energy of reactants and products, the activation energy, and the overall energy change.
Why is the activation energy important in a chemical reaction?
It determines the rate of reaction — higher activation energy means fewer particles have enough energy to react.
What type of reaction is combustion?
Exothermic, as it releases heat when substances burn.
What is thermal decomposition, and is it exothermic or endothermic?
Thermal decomposition is when a compound breaks down due to heat. It is an endothermic reaction because heat is absorbed.
How does bond energy relate to reaction type?
If more energy is required to break bonds than to make bonds, the reaction is endothermic.
If more energy is released in making bonds, it is exothermic.
Why are catalysts useful in reactions with high activation energy?
Catalysts lower the activation energy, allowing reactions to occur more easily and faster.
What is the bond energy of a chemical bond?
The amount of energy needed to break 1 mole of a particular bond in kilojoules (kJ/mol).
How do you experimentally determine if a reaction is exothermic or endothermic?
Measure the temperature change of the surroundings during the reaction.
Increase = Exothermic
Decrease = Endothermic
