Unit 5- Energy Changes and reversible reactions Flashcards
State the law of conservation of energy.
Energy cannot be created or destroyed, it can only transferred from one place to another.
How does the law of conservation of energy apply to chemistry?
In all chemical reactions, energy is either transferred to the surroundings or from the surroundings.
What is an exothermic reaction?
A reaction where energy is transferred to the surroundings.
Give two examples of exothermic reactions.
Combustion, respiration
What happens to the temperature of the surroundings during an exothermic reaction?
They increase. The thermometer is included in “the surroundings” so shows the temperature increasing.
What is an endothermic reaction?
A reaction where energy is transferred from the surroundings.
Give two examples of endothermic reactions.
Thermal decomposition reactions, citric acid and sodium hydrogencarbonate.
What happens to the temperature of the surroundings during an endothermic reaction?
They decrease. The thermometer is included in “the surroundings” so shows the temperature decreasing.
State two uses of exothermic reactions
Self-heating cans, hand warmers
State two uses of endothermic reactions
Some cooling sports injury packs
What are reactants?
The substances involved in a chemical reaction
What are products?
The substances formed when reactants have a chemical reaction
What is a reaction profile?
A diagram which shows whether the reactants have more or less energy than the products.
If the reactants have more energy than the products, what kind of a reaction must have taken place?
An exothermic one. The missing energy has been transferred to the surroundings.
If the reactants have less energy than the products, what kind of a reaction must have taken place?
An endothermic one. The extra energy has been take in by the surroundings.
Is breaking bonds endothermic or exothermic?
Endothermic. Chemical bonds are strong so require energy to break (like when you have to put energy in to separate magnets from each other)
Is making bonds endothermic or exothermic?
Exothermic. Energy is released when chemical bonds are formed (like how two magnets move together when close and generate kinetic energy)
How do we work out the overall energy change of a reaction?
Work out the difference between the energy needed to break all the bonds in the reactants and the energy released to form all the bonds in the products.
What is a reversible reaction?
A reaction which can go from reactants to products but also from products to reactants
What chemical symbol represents a reversible reaction?
⇌
If a reaction is exothermic in the forward direction what will it be in the reverse direction?
Endothermic
Two reactants require 30kJ to turn into products. What energy transfer is involved when the products turn into reactants?
30kJ is released
What is equilibrium?
The point in a reversible reaction when the forward and reverse reactions are occurring at the same rate
How is the amount of reactant changing at equilibrium?
The point in a reversible reaction when the forward and reverse reactions are occurring at the same rate
What is Le Chatelier’s principle?
When a reaction at equilibrium is changed, it will seek to counteract that change
How is the amount of reactant changing at equilibrium?
It is not changing
How is the amount of product changing at equilibrium?
It is not changing
A reaction is exothermic in the forward direction. What will occur if the temperature is increased?
The backward reaction will increase as it is endothermic and will reduce the temperature
A reaction is at equilibrium when some product is removed. What will occur?
The forward reaction will increase as that will increase the amount of product
The reaction below is at equilibrium. What will occur when the pressure is increased? 2H₂(g) + O₂(g) ⇌ 2H₂O(g)
The forward reaction will increase as there are fewer molecules on the right. This will reduce the total number of molecules and therefore the pressure.
