19 - Heat Energy Changes in Chemical Reactions Flashcards
What is anEndothermic reaction?
Energy is transferred from stores of energy in chemical bonds to the surroundings
What is anExothermic reaction?
Energy is transferred from stores of energy in chemical bonds to the surroundings
What is a Reaction profile?
A diagram to show how the energy stores in a substance changed during the course of a chemical reaction
What is Activation energy?
The minimum amount of energy needed to start a reaction
Endothermic reaction
Label where the activation energy & the overall energy change should go?
Exothermic Reaction
Label where the activation energy & the overall energy change should go?
Enodthermic or Exothermic?
Breaking bonds
Endothermic
Enodthermic or Exothermic?
Making bonds
Exothermic
How is temperature affected in an exothermic reaction?
Temperature INCREASES
How is temperature affected in an endothermic reaction?
Temperature DECREASES
Give some examples of reactions in which there are heat changes:
And how can these heat changes be demonstrated?
- Salts dissolving in water
- Neutralisation reactions
- Displacement reactions
- Precipitation reactions
Temp changes can be measured to show heat changes (only in a solution)
What is a Neutralisation reaction?
Reaction between an ACID and a BASE
Is a Neutralisation reaction endothermic or exothermic?
Exothermic
What is a Displacement reaction?
Reaction between a METAL and a COMPOUND OF A LESS REACTIVE METAL
or
between a HALOGEN and a COMPOUND OF A LESS REACTIVE HALOGEN
Is a Displacement reaction endothermic or exothermic?
Exothermic
What is a Precipitation reaction?
An insoluble product forms from 2 solutions
Is a Precipitation reaction endothermic or exothermic?
Endothermic or Exothermic
Depending on the substances used
Is salts dissolving in water
endothermic or exothermic?
Endothermic or Exothermic
Deoending on the salt
What is Bond energy?
The energy needed to break one mole of a specific covalent bond
What is Bond energy measured in?
Kj mol^-1
or
Kj/mol
The ^ symbolises ‘to the power of …’
How would you calculate Energy change in bond energy calculations?
Energy change = Energy IN - Energy OUT
Using this example, describe the process of calculating the energy change
You do NOT have to work anything out. Just describe the steps
If a bond energy calculation is negative is it endothermic or exothermic?
Exothermic
If a bond energy calculation is positive is it endothermic or exothermic?
Endothermic
What does it mean if the overall heat energy change for a reaction is exothermic?
If MORE heat energy is released in forming bonds in the products than is required in breaking bonds in the reactants
What does it mean if the overall heat energy change for a reaction is endothermic?
If LESS heat energy is released in forming bonds in the products than is required in breaking bonds in the reactants
