C7 - Energy Changes Flashcards
Hat is an exothermic reaction?
A reaction which transfers energy to the surroundings.
What happens to the the temperature in an exothermic reaction?
It rises
What are some examples of exothermic reactions?
Combustion
Neutralisation reactions (acid + alkali)
Oxidation reactions
What is an endothermic reaction?
A reaction that takes in energy from the surroundings
What happens to the temperature in a endothermic reaction?
It falls
What is are some examples of an endothermic reaction?
Thermal decomposition
Electrolysis
What are reaction profiles?
Diagrams that show the relative energies of the reactants and products, and how energy changes throughout the reaction
How would you know if a reaction profile is exothermic?
The products are at a lower energy than the reactants.
What reprsents the activation energy on reaction profile diagrams?
The intial rise of energy needed to start the reaction
What is activation energy in depth?
The minimum amount of energy needed for the reactants to collide with each other and react
The greater the activation energy, the more _____________________________________
Energy needed to start the reaction
How would you know if a reaction profile is endothermic?
The products are at a HIGHER energy than the reactants.
What happens to bonds during chemical reactions?
Old bonds are broken and new bonds are formed
Energy must be ________ to break existing bonds
Supplied
Energy is ________ when new bonds are formed
Released
Energy must be SUPPLIED to break existing bonds.
What reaction process is bond breaking?
Endothermic process
Energy must be RELEASED to form new bonds.
What reaction process is bond formation?
Exothermic process
What is thr ‘Bond Energy’?
The amount of energy needed to break one mole of a covalent bond
What is a fuel cell a type of?
Type of electochemical cell
Why are fuel cells a type of electrochemical cell?
They convert chemical energy of a fuel and oxygen into electrical energy that we use to power things
Explain the Temperature change Practical from C7.
- Measure 25cm3 of dilute HCL acid and put it into a polystyrene cup
- Place the cup into a glass beaker and record its temperature
- Now use a measuring cylinder to transfer 5cm3 of sodium hydroxide into the polystyrene cup
- Place a lid over the cup and poke a thermometer to record the temp rise
- Record the highest temp reached and then repeat with different volumes of Sodium hydroxide (going up in 5cm3)
Why do you use polystyrene cup in the temperature change practical?
Polystyrene is a good thermal insulator
Why does an exothermic reaction release energy to the surroundings?
the energy released when new bonds form is greater than the energy needed to break the original bonds
