C7+8 - Energy Changes Flashcards
What is an example of an exothermic reaction?
Wood burning (combustion), neutralisation and oxidation
What is an exothermic reaction?
Exothermic reactions transfer energy to the surroundings usually by heating with the temperature rising
Label and draw an energy change diagram for an exothermic reaction and compare it to real answer from textbook/revision guide
.
Where can we find practical uses for exothermic reactions?
Hand warmers and self heating cans
What is an endothermic reaction?
Endothermic reactions take in energy from the surroundings. The temperature tends to fall and it gets colder
What is an example of an endothermic reaction?
Thermal decomposition
What is the activation energy?
The minimum amount of energy that particles must have for a reaction
In the required practical when investigating temperate changes, what is the use of the polystyrene cup?
To give more insulation
Why do we put a lid on the beaker?
To reduce the energy lost by evaporation
What is the dependant variable in the practical?
The maximum temperature
What is the independent variable in this experiment?
The volume of sodium hydroxide
What is the control variable in the practical?
The volume of the hydrochloric acid and the concentration of the sodium hydroxide and hydrochloric acid
What is the method to this practical?
1) First we measure 30 cm cubed of HCL
2) Transfer it into a polystyrene cup then stand it in a beaker
3) Measure the temperature of the HCL and note this down in a table
4) Measure 5cm cubed of sodium hydroxide into the cup
5) Put a lid on the solution and put a thermometer in the mixture and record the temperature every 30 seconds recording the highest temp
What kind of reaction do we get when we break a chemical bond and why?
It’s an endothermic reactions as it requires energy and they are shown as positive
What reaction is it when we make chemical bonds?
Exothermic as we release energy therefore energy is shown as negative
