NATURAL SCIENCE. UNIT 5 SUMMARY- MATTER AND HEAT

 

NATURAL SCIENCE UNIT 5 SUMMARY: MATTER AND ENERGY

*This is just a summary. Don´t forget to study from your Pupil’s Book and your worksheets as well!

1. SEPARATING MIXTURES

A mixture is a combination of two or more substances. There are two types of mixtures:

a)     Heterogeneous mixtures: we see the various substances because they are not combined evenly. Example: fruit salad.

 

b)    Homogeneous mixtures: we can´t see the different substances because they are more closely combined. Example: orange juice.

 

We can use various methods to separate the components of a mixture (DON´T FORGET TO STUDY THE EXPLICATIVE DRAWINGS FROM YOUR WORKSHEET!):

1.MAGNETIC SEPARATION

It is used in heterogeneous mixtures to separate magnetic materials (some metals such as copper or iron) from non-magnetic materials (such as paper or plastic). A magnet attracts the magnetic materials, separating them from the non-magnetic materials.

 

2. DECANTATION

2.1 Separating solids from liquids

In a heterogeneous mixture, made up of a solid and a liquid (example: water and sand), we use decantation to separate both substances. We decant the liquid into another container and the sand (sediment) will remain in the previous container. This technique is not very accurate.

2.2 Separating two liquids of different density.

In a heterogeneous mixture, made up of two liquids with different densities (for example oil and water), we use decantation to separate both substances. The oil floats because it has lower density than the water. We decant the oil into another container and the water will remain in the previous one. Again, this technique is not very accurate.

 

3. FILTRATION

3.1. Separating solid particles from gases

The air is a heterogeneous mixture made of gases and solid particles such as dust or viruses. We use a filter (mask) to filter the air. The gases such as oxygen or carbon dioxide pass through the mask and the solid particles remain on the filter.

 

3.2 Separating solid particles from liquids

When we have a heterogeneous mixture made up of a liquid and a solid, for example pasta and water, we use the filtration technique to separate both substances. In this case, we use a filter (kitchen strainer). The water passes through the filter and the solid particles (pasta), remain in the filter.

 

4. EVAPORATION

It is used to separate two substances from a homogeneous mixture called solution (solid and a liquid). Example: salt and water.

The water evaporates at 100ºC and turns into vapour (gaseous state). The salt remains in a solid state as a sediment.

 

5. DISTILLATION

It is used to separate two liquids that have different boiling points (Example: water and ethanol).

Water evaporates at 100ºC and ethanol evaporates at 78ºC. If we apply thermal energy, the ethanol evaporates first and turns into the gaseous state. The water remains in a liquid state. Then, we cool down the gaseous ethanol and turn it into the liquid state.

 

2. PHYSICAL CHANGES

1. Changes in state

When a physical change takes place, the composition of the substance doesn´t change. Water is still water even though it can appear in a solid, liquid or gaseous state. (H2O)

Water evaporates at 100ºC and freezes at 0ºC.

PHYSICAL STATE	BEHAVIOUR OF THE ATOMS	SHAPE	VOLUME
SOLID	Atoms are packed together tightly and do not move around much.	stable	stable
LIQUID	Atoms are close together, but move around freely.	Non stable	stable
GAS	Atoms are further apart and move quickly in all directions.	Non stable	Non stable

 

2. Types of physical changes

a) Reversible changes: these changes are temporary and can be reversed. Example: when we freeze liquid oranges juice, it turns into an ice lolly. If we melt it, it will go back to a liquid state.

b)Irreversible changes: These changes are permanent and can´t be reversed. For example, if we cut a piece of paper, it will never go back to its original shape.

 

3. Mass, volume and density.

a) Mass: it is the amount of matter that an object contains. Grams (g) and kilograms (kg)

b)Volume: it is the amount of physical space that an object occupies . Litres (l) and millilitres (ml)

c)Density: it is the amount of matter that occupies a space. (g/ml or kg/l)

D= m/V

 

3. CHEMICAL REACTIONS

When a chemical reaction takes place, the composition of the original substance changes.

(DON´T FORGET TO STUDY THE FORMULA OF EACH REACTION!)

1.     COMBUSTION

It occurs when a fossil fuel (coal, natural gas, petrol, wood), burns thanks to the oxygen, and produces waste products such as carbon dioxide, solid particles (dust, ashes) and other gases. It also produces a lot of energy in the form of light and heat.

 

2.     OXIDATION

It occurs when some metals such as copper or iron react with oxygen. As a result, they turn into an oxide (“rust”)

 

3.     FERMENTATION

a)     When dough (flour, water and salt) reacts with yeast (fungi), it turns into fermented dough. The yeast produces carbon dioxide, and as a result, the dough rises.

b)    When milk reacts with bacteria (lactobacillus), it ferments producing lactic acid. As a result, we obtain dairy products such as yoghurt or cheese.

 

4.   FORMS OF ENERGY

Energy is never created or destroyed, only transformed.

1.     POTENTIAL ENERGY

It is stored in matter which is not moving. It can be changed into other types of energy.

2.     KINETIC ENERGY

It comes from motion or movement and it depends on both mass and speed.

3.     MECHANICAL ENERGY

It is the sum of potential and kinetic energy that is used to do a work.

4.     ELECTRICAL ENERGY

It comes from the flow of electrons from one atom to another.

5.     CHEMICAL ENERGY

It is released during chemical reactions

6.     LIGHT ENERY

It can be natural or artificial. We can see it with our eyes.

 

7.     SOUND ENERGY

It is produced from vibrations that we can detect with our ears or bodies.

 

8.     THERMAL ENERGY

Heat is thermal energy that flows from warmer objects to cooler objects.

 

 

5.   LIGHT

Light is form of energy that illuminates objects around us. It travels at 300.000km/s.

 

1.     LIGHT AND COLOUR

The Sun light looks white, but is made up of seven colours. We use a prism to separate the white light into the 7 colours.

We can combine the three primary colours (red, blue and yellow) to make white light.

 

Light travels in a straight light until it hits an object. We only see the colours that are reflected.  For example: if we see strawberries red it’s because, they are reflecting the red colour and absorbing the others.

 

2.     REFLECTION

a)     When light hits a smooth surface, all they rays reflect in one direction. Clear images are obtained. (Mirror)

b)    When light hits a rough surface, the rays reflect in many different directions. It doesn´t reflect clear images (Concrete, wood)

 

3.     REFRACTION

It happens when light changes direction as passes from one material to another. Example: when we introduce a spoon in a glass of water, it looks bent, but it’s just an optic effect. The direction of the light is changing as it passes from the air to the water.

 

A lens is a curved piece of glass or transparent plastic that refracts light and can make objects look bigger or smaller. They are used in many devices such as binoculars, eyeglasses, cameras…

There are two types of lenses:

a)     Convex lenses: also called positive lenses, bend the light inwards. (Magnifying glasses or microscopes)

b)    Concave lenses: also called negative lenses, spread the light outwards (projectors).

 

4.     ELECTRICITY FROM LIGHT

Solar panels use sunlight to generate power. The sunlight is absorbed by photovoltaic cells, which convert it into electricity.

Photovoltaic power stations have many solar panels that can produce enough electricity for thousands of homes.

 

6.   HEAT

Matter is composed of small particles that are always moving.

This produces thermal energy, which flows as heat from one particle to another.

The temperature of a material depends on how much thermal energy its particles have.

 

1.     HEAT TRANSFER

When particles come together, the hotter and faster-moving particles transmit energy to the cooler and slower-moving particles.

A substance reaches the thermal equilibrium when all its particles have the same temperature.

 

Heat can be transferred in three ways:

a)     radiation: some heat sources produce thermal energy in the form of radiation (gas cookers). This energy is transferred to other objects at a distance, without any physical contact.

 

 

b)    conduction: heat is transferred when a heat source comes into contact with another object. Dense materials such as metals are good conductors because their particles are close together.

 

c) convection: when liquids and gases heat up, their particles become less dense and rise. When the particles lose heat, they sink down again. This circular movement is called convection.

 

 

2.     CONDUCTORS AND INSULATORS.

a)     Thermal conductors: they transfer heat very effectively. (Metals such as iron, copper)

b)    Thermal insulators: they don´t transfer heat very effectively.

(Plastic or wool)

 

 

3.     EFFECTS OF THERMAL ENERGY

a)Expansion: when we heat a substance, it volumes increases and they expand. Example: galio thermometer.

 

b)Melting: solids melt and become liquids when we heat them  to their melting point. Example: melting chocolate

 

c)Evaporation: liquids evaporate and become gases when we hit them to their boiling point. Example: boiling water.