P3 Internal Energy and Changes of State (page 193) Flashcards
Look at the specific heat capacity notes on p.169 before you start - you need to understand it and be able to use ∆E = mc ∆θ for this topic.
Internal Energy is the Total Energy stored by what?
Particles in a System
What do particles do in a system?
they vibrate or move around - they have energy in their kinetic energy stores.
Apart from kinetic energy stores, particles also have energy in their potential energy stores, why?
this is due to their positions.
Where is the energy stored in a system?
it is stored by its particles (atoms and molecules).
The internal energy of a system is the total energy that its particles have in their kinetic and potential energy stores.
Heating the System, transfers energy to its particles, how?
they gain energy in their kinetic stores and move faster, increasing the internal energy. (see picture 1 on page 193).
This leads to a change in temperature or a change in state. If the temperature changes, the size of the change depends on the mass of the substance, what it’s made of (its specific heat capacity) and the energy input.
(make sure you remember all the stuff on a specific heat capacity from p.169, particularly how to use the formula).
A change in state occurs if the substance is heated enough, how?
the particles will have enough energy in their kinetic energy stores to break the bonds holding them together.
When you heat a liquid what happens?
it boils (or evaporates) and becomes a gas.
When you heat a solid what happens?
it melts and becomes a liquid.
What is meant by a change of state?
when a solid heats up and then melts/when a liquid is heated up and it boils or evaporates and becomes a gas.
Can a change of state happen during cooling?
Yes. The particles lose energy and form bonds.
What are the changes of state?
look at diagram 2 on page 193.
Is a change of state a physical change or chemical change?
it is a physical change. This means you don’t end up with a new substance - it’s the same substance as you started with, just in a different form.
If you reverse a change of state (e.g. freeze a substance that has been melted), what will happen to the substance?
it will return to its original form and get back its original properties.
If a change of state happens, do the number of particles change, explain your answer?
No they don’t change - they’re jst arranged differently. This means mass is conserved - non of it is lost when the substance changes state.
During an experiment, a solid is heated until it melts into a liquid. Explain how heating the solid causes this change of state (3 marks)
Heating the solid transfers energy to the kinetic energy stores of the particles (increasing the internal energy) (1 mark).
When the particles have enough energy in their kinetic energy stores, they can break the bonds holding them together (1 mark)
The solid changes state and becomes liquid (1 mark).
