TOPIC C5 - ENERGY CHANGES Flashcards
Give the definition of exothermic
In an exothermic reaction, heat/energy is often released to the surroundings, we see this as a temperature rise
Give the definition of endothermic
In an endothermic reaction heat/energy is absorbed from the surroundings, we see this as a temperature decrease
Give two examples of an exothermic reaction
Combustion, neutralisation reactions between acids and alkali
Give two examples of an endothermic reaction
reaction between citric acid + sodium hydrogencarbonate, thermal decomposition
What does it mean if products of a reaction store more energy than the reactants? Would this be an endothermic or exothermic reaction?
They have taken in the difference in energy between the products and reactants from the surroundings during the reaction - endothermic.
What does it mean if products of a reaction store less energy than the reactants? Is it an exothermic or endothermic reaction?
They have transferred excess heat/energy to the surroundings during the reaction - exothermic.
Why does the amount of energy in the universe always stay the same?
Energy cannot be created nor destroyed - it can only be moved around
How can you measure energy transfer? What does this method work for?
Take the temperature of the reagents, mix them in a polystyrene cup and measure the temperature of the solution at the end of the reaction
This method works for neutralisation reactions or reactions between metals and acids or carbonates and acids.
What is the biggest problem when measuring energy transfer and how can you solve it?
The amount of energy lost to the surroundings
You can reduce it a bit by putting the polystyrene cup into a beaker of wool to give more insulation and putting a lid on the cup to reduce energy lost by evaporation.
State what reaction profiles show
The relative energies of the reactants and products in a reaction and how the energy changes over the course of the reaction - represent wether its an endothermic or exothermic reaction
In what reaction profile are the products at a lower energy than the reactants?
Exothermic profile
What is the initial rise in energy on the reaction profile?
Represents the energy needed to start the reaction - this is called activation energy
What is the activation energy?
the minimum amount of energy the reactants need to collide with each other and react.
the greater the activation energy the more energy needed to start the reaction, this has to be supplied eg by heating the reaction mixture.
What reaction profile has products higher than than the reactants?
endothermic profile
state what the difference in height represents in an endothermic profile diagram
the overall energy change in the reaction - the energy absorbed
