# 4 Energy resources and energy transfers

## 4.01 use the following units: kilogram (kg), joule (J), metre (m), metre/second (m/s), metre/second2 (m/s2), newton (N), second (s) and watt (W)

know the units for

Mass = kilogram (kg)

energy = joule (J)

velocity = metre/second (m/s)

acelleration = metre/ second 2 (m/s2)

force = newton (N)

time = second (s)

power = watt (W)

## 4.02 describe energy transfers involving energy stores: energy stores: chemical, kinetic, gravitational, elastic, thermal, magnetic, electrostatic, nuclear and energy transfers: mechanically, electrically, by heating, by radiation (light and sound)

 Energy Stores: Chemical – e.g. the food we eat Kinetic – movement energy Gravitational – objects that are lifted up Elastic – e.g. from springs Thermal – from hot objects Magnetic – objects in magnetic fields Electrostatic – charged objects Nuclear –  stored within a nucleus

## 4.05 describe a variety of everyday and scientific devices and situations, explaining the transfer of the input energy in terms of the above relationship, including their representation by Sankey diagrams The energy flow is shown by arrows whose width is proportional to the amount of energy involved. The wasted and useful energy outputs are shown by different arrows.

## 4.06 describe how thermal energy transfer may take place by conduction, convection and radiation

Conduction is the transfer of thermal energy through a substance by the vibration of the atoms within the substance. Metals are good conductors because they have free electrons that can move easily through the metal, making the transfer of energy happen faster.

Convection occurs in a liquid or gas. These expand when heated because the particles move faster and take up more volume – the particles remain the same size but become further apart. The hot liquid or gas is less dense, so it rises into colder areas. The denser, colder liquid or gas falls into the warm areas. In this way, convection currents are set up which transfer heat from place to place.

Thermal radiation is the transfer of energy by infrared (IR) waves. These travel very quickly in straight lines.

## 4.08 explain how emission and absorption of radiation are related to surface and temperature

 –          Light, shiny surfaces are good reflectors of IR and so are poor at absorbing it. –          Dark, matt surfaces are poor reflectors and good at absorbing IR. –          This means that placed next to a heat source, a dark object would heat up faster than a light one. –          Dark matt surfaces are also best at emitting IR. This means that a hot object with a light shiny surface will emit less IR than a dark matt object at the same temperature. –          Hotter objects emit more IR per second. The type of EM wave emitted also changes with temperature – the higher the temperature the higher the frequency of EM wave emitted.

## 4.09 practical: investigate thermal energy transfer by conduction, convection and radiation   Select a set of flashcards to study:

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Section 1: Principles of chemistry

a) States of matter

b) Atoms

c) Atomic structure

d) Relative formula masses and molar volumes of gases

e) Chemical formulae and chemical equations

f) Ionic compounds

g) Covalent substances

h) Metallic crystals

i) Electrolysis

Section 2: Chemistry of the elements

a) The Periodic Table

b) Group 1 elements: lithium, sodium and potassium

c) Group 7 elements: chlorine, bromine and iodine

d) Oxygen and oxides

e) Hydrogen and water

f) Reactivity series

g) Tests for ions and gases

Section 3: Organic chemistry

a) Introduction

b) Alkanes

c) Alkenes

d) Ethanol

Section 4: Physical chemistry

a) Acids, alkalis and salts

b) Energetics

c) Rates of reaction

d) Equilibria

Section 5: Chemistry in industry

a) Extraction and uses of metals

b) Crude oil

c) Synthetic polymers

d) The industrial manufacture of chemicals