4. Energetics
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What is energy transfer during a reaction due to?
The breaking and forming of bonds
What happens to energy when bonds are broken?
Energy is taken in
What happens to energy when bonds are formed?
Energy is released
In terms of bonds, when is energy taken in?
When bonds are broken
In terms of bonds, when is energy released?
When bonds are formed
What is stored energy known as?
Enthalpy
What is the symbol for enthalpy?
H
What is enthalpy?
Stored energy
Can enthalpy be measured?
No
How can enthalpy changes be found?
By measuring the change in temperature during reactions - at a constant pressure
What must be constant when measuring change in temperature to work out enthalpy change?
Pressure
What is the mnemonic to remember energy when breaking/making bonds?
Bendy Mexicans breaking = endo, making = exo
What happens to energy in an endothermic reaction?
It is taken in
When energy is taken in during an endothermic reaction, what form does it usually take?
Heat
What happens to the temperature of the surroundings during an endothermic reaction?
It decreases
What is higher in an endothermic reaction; the energy to make bonds or to break them?
Energy to break bonds is higher than to make them
What does it mean, in terms of energy, that endothermic reactions need more energy to break bonds than to make them?
There is an overall need for energy for the reaction to take place = positive ΔH value
Why do endothermic reactions have a positive ΔH value?
There is an overall need for energy in order for the reaction to take place - so the system gains energy
Do endothermic reactions have a positive or negative ΔH value?
Positive
What happens to energy in an exothermic reaction?
It is released
When energy is released during an endothermic reaction, what form does it usually take?
Heat
What happens to the temperature of the surroundings during an exothermic reaction?
It increases
Why does the temperature of the surroundings increase during an exothermic reaction?
Energy is transferred to the surroundings
What is higher in an exothermic reaction; the energy to make bonds or to break them?
The energy when making bonds