Science Sem 2 Exam (Chemistry, Waves and Greenhouse gases)

What are reactants in a chemical equation?

The starting substances before a chemical reaction takes place, written on the left.

What are products in a chemical equation?

The new substances formed as a result of a chemical reaction, written on the right.

What does the arrow mean in a chemical equation?

It shows a reaction taking place, meaning 'react to produce'.

What is the general layout of a chemical equation?

Reactants -> Products

What is a chemical compound?

A substance made from two or more different types of element chemically bonded together.

What is a chemical bond?

A strong force that holds atoms together in a compound.

What is an element?

A pure substance made of only one type of atom.

What is a chemical symbol?

One or two letters used to represent a type of atom.

What does a chemical formula indicate?

The chemical symbols and numbers telling how many of each atom are present.

What do subscript numbers in a formula represent?

The number of atoms of that element in a molecule.

How many naturally occurring elements are there?

92

Where are the different types of elements listed?

The Periodic Table of elements.

What is a molecule?

A particle made of two or more atoms chemically joined together.

What is the chemical formula for water?

H2O

What is the chemical formula for carbon dioxide?

CO2

What is the chemical formula for methane?

CH4

How many different elements are in H2SO4?

Three.

What is the word equation for methane burning in oxygen?

Methane + oxygen -> carbon dioxide + water.

What is the Law of Conservation of Mass?

No new matter is created or destroyed during a chemical reaction; atoms are just rearranged.

What does a coefficient indicate in a chemical equation?

It indicates how many molecules or atoms of a substance there are.

What are some common indicators or evidence of a chemical reaction?

Colour changes, light production, scent production, bubbles, and temperature changes.

What do the state symbols (s), (l), and (g) represent in a chemical equation?

Solid, liquid, and gas respectively.

Why must a chemical equation be balanced?

To ensure that the number of each atom is the same on both sides of the reaction arrow.

Atoms

The basic building block of all matter.

Subatomic Particles

The particles that make up an atom, such as protons, neutrons and electrons.

Chemical change

An irreversible action where atoms of reactants are rearranged to form new products. Signs include, Bubbles, Odour, Light, Temperature change, Colour change, Precipitate and New product formed

Physical change

The state of matter changes, for example like ice -> water -> steam

Endothermic

A chemical reaction that produces a cool environment.

Exothermic

A chemical reaction that produces a hot environment.

Frequency

The number of waves passing a point each second

Wavelength

The distance between one wave crest and the next

Mechanical wave

A wave that requires a medium to travel

Electromagnetic wave

A wave that can travel through a vacuum

Transverse wave

A wave where particles move at right angles to the direction of wave travel

Longitudinal wave

A wave where particles move in the same direction as the wave

Reflection

Light bouncing off a surface

Refraction

The bending of light as it passes from one material to another

Transparent

Allows most light to pass through

Translucent

Allows some light through, producing a blurred image

Opaque

Does not transmit light

Convex lens

A lens thicker in the middle that converges light

Concave lens

A lens thinner in the middle that diverges light

What happens to particles when a substance is heated?

They vibrate faster.

What is temperature?

A measure of how fast the particles are moving on average.

What is thermal conduction?

The transfer of thermal energy by the vibration of particles, occurring most easily in solids.

What is a thermal conductor?

A material that transfers thermal energy quickly from hot to cold (e.g., metals).

What is a thermal insulator?

A material that is a very poor thermal conductor and transfers energy slowly (e.g., plastic and wood).

What is a fluid?

A substance that can flow, which includes both liquids and gases.

Why do warm fluids rise?

When heated, they expand and become less dense than the surrounding fluid, causing them to float upwards.

What is a convection current?

A current formed when warm, less dense fluid rises and cooler, denser fluid sinks to take its place.

What is radiation?

The transfer of thermal energy through infrared electromagnetic waves that can travel through space without direct contact or a medium.

What do waves transfer?

Energy (waves do not transfer particles).

What is a medium?

A substance or material that waves travel through.

Why can light travel through a vacuum while sound cannot?

Light is an electromagnetic wave that does not need a medium, whereas sound is a mechanical wave requiring a medium.

What is an oscillation?

A regular, repeating back-and-forth motion around a central point.

What is a transverse wave?

A wave where the oscillations are perpendicular to the direction of wave travel.

What is a longitudinal wave?

A wave where the oscillations are parallel to the direction of wave travel.

What is a compression in a longitudinal wave?

A region where the particles are pushed close together.

What is a rarefaction in a longitudinal wave?

A region where the particles are spread further apart.

What type of wave is light?

A transverse electromagnetic wave.

What type of wave is sound?

A longitudinal mechanical wave.

What effect does increasing amplitude have on a sound wave?

It increases the volume.

What effect does increasing frequency have on a sound wave?

It increases the pitch.

What is ultrasound?

Sound waves with frequencies above 20,000 Hz.

What is infrasound?

Sound waves with frequencies below 20 Hz.

What part of the ear turns sound vibrations into electrical signals?

The cochlea.

What are the colours of the visible spectrum in order?

Red, orange, yellow, green, blue, indigo, violet.

Why does a blue object appear blue?

It reflects blue light and absorbs green and red.

What does transmission mean?

When light passes through a material without being absorbed or reflected.

What is a vacuum?

A space entirely devoid of matter.

How are the direction of the oscillation and direction of wave related in a transverse wave?

They are oscillating at right angles to the direction of the wave.

What are the three types of mediums?

Transparent, translucent, opaque.

What is transmission?

A wave passing all the way through the medium.

What is reflection?

A wave bounces back off the medium.

What is absorption?

A wave is absorbed by the medium. it doesn't pass through the medium but it also doesn't get reflected.

How are the direction of oscillations and direction of wave related in a longitudinal wave.

The are oscillating in the same direction of the of wave.