Cambridge IGCSE Chemistry - States of Matter, Elements, Compounds, and Mixtures

Flashcards covering States of Matter, Kinetic Particle Theory, Changes of State, Gas Behavior, Diffusion, Elements, Compounds, and Mixtures from Cambridge IGCSE Chemistry lecture slides.

How is matter defined in chemistry?

Matter is defined as any substance that has mass and occupies space.

What are the shape, volume, and compressibility properties of solids, liquids, and gases?

Solids have a fixed shape, fixed volume, and cannot be compressed. Liquids have no fixed shape, fixed volume, and cannot be compressed. Gases have no fixed shape, no fixed volume, and can be compressed.

What is the core statement of the kinetic particle theory?

The kinetic particle theory states that all matter is made up of tiny particles that are in constant random motion.

How are particles arranged and how do they move in a solid?

In a solid, particles are closely packed, held together by very strong forces of attraction, and can only vibrate and rotate about their fixed positions.

Why does a solid have a fixed volume and resist compression?

A solid cannot be compressed and has a fixed volume because its particles are packed very close to one another with minimal space between them.

How are particles arranged and how do they move in a liquid?

In a liquid, particles are arranged in a disorderly manner, packed quite closely together, held by weaker forces of attraction than in a solid, and move freely throughout the liquid.

How are particles arranged and how do they move in a gas?

In a gas, particles are spread far apart from one another, have weak forces of attraction, possess high kinetic energy, and move rapidly in all directions.

What are three key differences between boiling and evaporation?

Boiling occurs only at the boiling point, occurs throughout the liquid, and happens rapidly. Evaporation occurs at temperatures below the boiling point, occurs only at the surface of the liquid, and happens slowly.

How does kinetic particle theory explain the process of melting?

When a solid is heated, its particles absorb heat energy and vibrate faster. At the melting point, the vibrations become sufficient to overcome the attractive forces holding the particles in fixed positions, allowing them to break away and move freely as a liquid.

Why does the temperature of a substance remain constant during melting on a heating curve?

The heat energy absorbed by the solid is used to overcome the forces of attraction holding the particles in fixed positions rather than increasing the kinetic energy and temperature.

Why does the temperature remain constant while a liquid freezes on a cooling curve?

Heat is released as particles are attracted to each other to settle into fixed positions to form a solid; this released heat offsets the thermal energy lost to the surroundings.

What is a volatile liquid?

A volatile liquid is a liquid that evaporates quickly at room temperature.

How does kinetic particle theory explain condensation?

When a gas cools, its particles give out heat and lose kinetic energy, moving more slowly until the attractive forces pull them close enough together to form a liquid.

What is the effect of increasing temperature on the volume of a gas at constant pressure, and why?

The volume of the gas increases because the gas particles gain kinetic energy, collide with greater force against each other and the container, and move further apart.

What is the effect of increasing pressure on the volume of a gas, and why?

The volume of the gas decreases because applying pressure causes the gas particles to collide more frequently and move closer together.

What is diffusion?

Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration.

How does relative molecular mass affect the rate of gas diffusion?

Gases with a lower relative molecular mass diffuse faster than gases with a higher relative molecular mass.

In the demonstration where concentrated aqueous ammonia ($\text{NH}_3$) and concentrated hydrochloric acid ($\text{HCl}$) diffuse in a tube, why does the white ring of ammonium chloride ($\text{NH}_4\text{Cl}$) form nearer the hydrochloric acid end?

Ammonia gas has a lower relative molecular mass ($\text{M}_r = 17$) than hydrogen chloride gas ($\text{M}_r = 36.5$), so ammonia particles travel and diffuse faster.

How does diffusion occur when a crystal of potassium manganate(VII) is placed in a beaker of water?

The crystal dissolves to form a deep purple solution at the bottom, and the particles gradually diffuse slowly throughout the water until the solution becomes uniformly purple.

What is an element?

An element is a pure substance that cannot be broken down into two or more simpler substances by chemical processes.

What rules must be followed when writing a two-letter chemical symbol for an element?

The first letter of the symbol is always in upper case and the second letter is always in lower case.

What is an atom, and what are monatomic elements?

An atom is the smallest particle of an element that retains the chemical properties of that element. Monatomic elements are elements that exist as individual uncombined atoms, such as the noble gases (helium, neon, argon, krypton, xenon, radon).

What is a molecule, and what defines a diatomic molecule?

A molecule is a group of two or more atoms that are chemically combined. A diatomic molecule is formed specifically by the combination of two atoms.

What is the difference between the chemical representations $\text{H}_2$ and $2\text{H}$?

$\text{H}_2$ represents one single molecule of hydrogen composed of two chemically combined hydrogen atoms, whereas $2\text{H}$ represents two separate individual hydrogen atoms.

Give three examples of elements that exist as molecules containing three or more atoms.

Ozone ($\text{O}_3$), phosphorus ($\text{P}_4$), and sulfur ($\text{S}_8$).

What is a compound?

A compound is a pure substance containing two or more elements that are chemically combined in a fixed ratio.

What two types of particles can make up a compound?

A compound can be made up of molecules (such as water) or ions, which are electrically charged particles carrying positive or negative charges (such as sodium chloride).

How do the properties of a compound differ from those of its constituent elements, using the reaction of magnesium and oxygen as an example?

A compound has properties distinct from its constituent elements. Silvery solid magnesium and colourless gas oxygen burn together to form magnesium oxide, which is a white solid.

Based on the provided diagram of lead(II) nitrate $\text{Pb(NO}_3\text{)}_2$, how many atoms of lead, nitrogen, and oxygen are present in one formula unit?

$1$ lead atom, $2$ nitrogen atoms, and $6$ oxygen atoms, giving an atomic ratio of $1 : 2 : 6$.

What is the ratio of carbon, hydrogen, and oxygen atoms in ethanol ($\text{C}_2\text{H}_5\text{OH}$)?

Carbon : Hydrogen : Oxygen = $2 : 6 : 1$.

What are the two main chemical processes used to decompose compounds into elements or simpler compounds?

Thermal decomposition (breaking down a compound using heat) and electrolysis (breaking down a compound using electricity).

What products are formed during the thermal decomposition of copper(II) carbonate as shown in the experimental setup?

Copper(II) oxide (solid) and carbon dioxide gas.

What is a mixture?

A mixture is made up of two or more substances that are not chemically combined.

What is an alloy, and which elements compose the alloy brass?

An alloy is a mixture of a metal with other metals or non-metals. Brass is an alloy made of copper and zinc.

How does the magnetic property differ between an unheated mixture of iron and sulfur and the compound iron(II) sulfide formed after heating?

In the mixture, iron retains its magnetic property and can be separated with a magnet. In contrast, the compound iron(II) sulfide has no magnetic properties.

How do mixtures and compounds differ regarding separation, properties, energy change, and composition?

Separation: mixtures are separated by physical processes, compounds only by chemical processes. Properties: mixtures have the same chemical properties as their components, compounds have different properties from constituent elements. Energy change: mixtures form with little/no energy change, compounds form with chemical reactions and significant energy change. Composition: mixtures have variable proportions, compounds have fixed proportions.