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Chemistry > Topic 3 - Physical and Chemical Changes > Flashcards

Topic 3 - Physical and Chemical Changes Flashcards

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1
Q

What are the features of a Physical Change?
And what are examples of a Physical Change?

A

Features: A physical change is:

  1. Reversible; and
  2. no new substances are formed.

Examples:

a. Boiling water;
b. Freezing water;
c. Melting water;
d. Dissolving sugar;
e. Crushing a pill;
f. Cutting hair

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2
Q

What are the features of a Chemical Change?
And what are examples of a Chemical Change?

A

Features: A chemical change is:

  1. Irreversible; and
  2. NEW substances are formed.

Examples:

a. Frying Egg/ Cooking;
b. Metal rusting;
c. Paper burning;
d. Photosynthesis.

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3
Q

What are the differences between Physical and Chemical Changes?

A

Physical Changes:

  1. No new substances are formed;
  2. Properties of the substances remain the same;
  3. Reversible

Chemical Changes:

  1. NEW substances are formed;
  2. Properties of the substances DO NOT remain the same/ are DIFFERENT;
  3. IRREVERSIBLE
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4
Q

How are new substances formed in a chemical change?

A

In a chemical change, atoms of chemical substances break apart and re-arrange to form new substances.

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5
Q

What is the role of energy in a chemical reaction?

A
  1. Many reactions need energy to get them started (eg Heat/ Light/ Electrical energy); and
  2. Many reactions give out heat energy once the reaction has started (eg burning of magnesium).
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6
Q

What are some signs of a chemical reaction?

A
  1. Heat energy being given out;
  2. Bubbling/ effervescence;
  3. Change of colour of the solution;
  4. Precipitation is formed.
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7
Q

What is a word equation?

Please give an example.

A

A word equation is a shorthand way of writing a chemical reaction.

Reactants → Products

Eg. Word equation for hydrogen reacting with oxygen is:

Hydrogen + Oxygen → Water

REACTANTS | PRODUCT

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8
Q

What is the Word Equation for Zinc reacting with Copper Oxide?

Which is the reactant and which is the product?

A

Zinc (Zn) + Copper Oxide (CuO) → Zinc Oxide (ZnO) + Copper (Cu)

REACTANTS | PRODUCTS

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9
Q

What are the causes of Chemical Changes?

A
  1. Heat
  2. Light
  3. Electrical energy;
  4. Mixing of Substances
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10
Q

What happens during chemical changes caused by heat?

A

Combustion is the scientific word for burning and is a type of chemical reaction.
During combustion, a substance burns and reacts with oxygen to produce light and heat (eg burning coal).

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11
Q

What is the substance that burns and reacts with oxygen called?

What are some examples of these substances?

A

The substance that burns in oxygen to give energy is called a FUEL.

Examples include coal, petrol, wood, methane, gas, ethanol/ alcohol – these provide more than 90% of the energy needed for transport, factories and in the home.

Most fuels contain the elements of carbon and hydrogen.

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12
Q

Describe the steps of combustion of Methane CH4 which is often burnt for cooking.

A
  1. Methanes is made up of Carbon and Hydrogen.
  2. It reacts with Oxygen when it burns.
  3. Carbon in CH4 changes into Carbon Dioxide when it burns in oxygen.
  4. Hydrogen in CH4 changes into water when it burns in oxygen.
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13
Q

What is the Word Equation for the combustion of Methane?

A

Methane + Oxygen → Carbon Dioxide + Water

REACTANTS | PRODUCTS

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14
Q

What are the different types of combustion, and
what are the byproducts?

A
  1. COMPLETE combustion – a fuel burns in sufficient amount of oxygen,
    and carbon dioxide (CO2) is formed. Water (H2O) may also be formed.
    Eg: Flame of a bunsen burner with air-hole opened.
  2. INCOMPLETE combustion – a fuel burns in insufficient amount of oxygen,
    and carbon monoxide (CO2) and/or soot (C) is formed.
    Eg: Flame of a bunsen burner with air-hole closed.

Effects of incomplete combustion can be seen in the laboratory Bunsen burner.

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15
Q

What is Thermal Decomposition?

Give 3 examples of Word Equations for Thermal Decomposition?

A

Thermal decomposition is the process where a single compound breaks down into 2 or more simpler substances.

Heat Heat

Sugar =====> Carbon + Water Vapour Calcium Carbonate =====> Carbon dioxide + Calcium oxide

Heat

Magnesium Hydroxide =====> Magnesium oxide + Water Vapour

Heat is also a REACTANT in these endothermic reactions (requires heat).

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16
Q

What kind of reaction is a Combination?

What are examples of combinations?

A

What is it?

A combination is also known as a synthesis reaction – it is a chemical reaction in which 2 or more substances combine to form a NEW COMPOUND.

Examples?

  1. Elements react together to form a new compound: a. Magnesium + Oxygen → Magnesium Oxide; b. H2O
  2. Compounds react together to form a new compound: a. Calcium Oxide + Water → Calcium Hydroxide
17
Q

What are examples of Chemical Changes caused by Light?

A
  1. Photosynthesis:

Light energy is absorbed by the chlorophyll in green plants to make glucose and oxygen from Carbon Dioxide and Water LIGHT
Carbon Dioxide + Water ==============> Glucose + Oxygen

  1. Film Photography

a. Black and white photographic film contains silver bromide coating which is sensitive to light.
b. When exposed to light, silver bromide decomposes into silver, which produces the dark areas on the film.
c. The stronger the light, the darker the area on the film (entirely black = overexposed to light).

LIGHT
Silver Bromide ==============> Silver + Bromine

18
Q

What happens during chemical changes caused by MIXING?

What are examples of such reactions?

A

Chemical changes can occur when we mix 2 or more substances together.

Examples:

  1. Mixing metal zinc + dilute Hydrochloric Acid → bubbles of gas (hydrogen) is formed.
  2. Mixing concentrated sulfuric acid + sugar → black substance (carbon) is formed.
  3. Mixing baking soda with vinegar → bubbles of gas (CO2) is formed.
19
Q

What happens during chemical changes caused by Electricity?

What are 3 examples of such reactions?

A

Electrolysis is the process of decomposing a substance into simpler substances by using electricity.

Examples:

  • *Electricity**
    a. Sodium chloride ==============> Sodium + Chlorine
  • *Electricity**
    b. Aluminum chloride ==============> Aluminium + Oxygen
  • *Electricity**
    c. Water ==============> Hydrogen gas (Negative electrode) + Oxygen gas (Positive electrode)

Water decomposes into hydrogen gas and oxygen gas when electricity passes through it.

20
Q

How do you test for gases?

A
  1. H2 - lighted splint extinguishes with a “pop” sound
  2. NH3 – moist/ damp red litmus paper turns blue
  3. CO2 – pass the gas into limewater; turns limewater milky or gives a white precipitate in limewater = Ca(OH)2
  4. O2 – a glowing splint will be rekindled/ relights
21
Q

How do you test for water H2O?

A
  1. Cobalt chloride test paper - turns from blue (dry) to pink (wet/moist)
  2. Dry copper sulfate – turns from white (dry) to blue (wet) when water is added.

Chemistry (2 decks)

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