3) Energy changes in industry Flashcards
How to calculate kelvin (K)?
⁰C to K = +273
What is the symbol for standard conditions?
⦵
What are the standard conditions?
Pressure-kPa
Temp- 293K (25C)
Concentration- 1 moldm-3
All reactants and products are in their standard states.
What is an exothermic reaction?
Exothermic reactions give out heat energy to the surroundings
What is an endothermic reaction?
Endothermic reactions take in energy from the surroundings
Why do exothermic reactions give out heat to their surroundings?
This is because the enthalpy of the products being made is smaller than the enthalpy of the reactants being used so the excess heat is released.
Why do endothermic reactions take in heat from their surroundings?
This is because the enthalpy of the products being made is bigger than the enthalpy of the reactants being used so additional heat is required from the surrounding area.
Are endothermic/exothermic have a positive/negative enthalpy change?
Exothermic- Negative Enthalpy change
Endothermic- Positive enthalpy change
What is enthalpy?
Heat content of reactions.
Why do exothermic reactions have a negative ΔH?
Because heat energy has been lost from the chemical system and released into the surroundings
Why do endothermic reactions have a positive ΔH?
Because heat energy has been gained by the chemical system from the surroundings
What activation energy?
The energy required for the reaction to take place (shown as Ea)
How do catalysts affect rate of reaction?
Catalysts increase the rate of chemical reactions by providing an alternative reaction route with a lower activation energy
What are the advantages of catalysts?
Don’t get used up
Can be reused
What are the two stages to dissolving an ionic solid?
Step 1: Breaking down the ionic lattice
Step 2: Hydration of the ions by water molecules
How is breaking down the ionic lattice endothermic?
Breaking down an ionic lattice requires a large input in energy in order to break the strong electrostatic forces of attraction between the oppositely charged ions. This process is therefore endothermic
What occurs during hydration?
The positive ions will be attracted to the δ- oxygen atom in the water molecules
The negative ions will be attracted to the δ+ hydrogen atoms in the water molecules
The water molecules will completely surround the ions
Why is hydration of the ions by water molecules exothermic?
This process involves the formation of new bonds therefore energy is released and therefore hydration of ions is always exothermic
What 2 things is the magnitude of the enthalpy change of hydration dependent on?
1)The size of the ions
2) The charge of the ions
How does the size of the ion affect the magnitude of the enthalpy change of hydration?
The smaller the ion the more exothermic the enthalpy change of hydration. This is because smaller ions have a higher charge density and can get closer to the water molecules. Therefore there is a stronger attraction between the ions and the water molecules
How does the charge of the ion affect the magnitude of the enthalpy change of hydration?
The higher the charge of the ion the more exothermic the enthalpy change of hydration. This is because ions with higher charges have a higher charge density and can get closer to the water molecules and are able to attract them more strongly
