Flashcards in Semester 2 - Chemistry Deck (63):
In a chemical reaction, the chemicals that are present to begin with are called what? What are the new chemicals made after the reaction called.
What happens during a chemical reaction to change the reactants to the products?
The bonds between the atoms of the reactants are broken and the atoms are rearranged to form new bonds, resulting in the formation of products. During a chemical reaction, atoms are neither created nor destroyed, they are simply rearranged.
What is the Law of Conservation of Mass? Who stated this?
It refers to the fact that the mass of the reactants will always equal the mass of the products. So, when writing a chemical equation for a reaction all atoms of each element on the left hand side of the equation must be present on the right side of the equation. Antoine-Laurent Lavoiser states this.
Give an example of the Law of Constant Proportions.
CO2 (small) - 2 atoms of oxygen will always bond with 1 atom of carbon.
What is one way to tell if a chemical change has occurred, and not just a physical change? Give an example of each.
In a chemical change, the reactants would be different to the products. An example is the chemical change of water into hydrogen peroxide. In a physical change, the products are the same as the reactants, but it may have an l (liquid) in brackets next to it, and not an s (solid) like on the left hand side. An example of a physical change is when water is frozen into ice.
What is a chemical reaction?
A sequence of symbols and formulas that show what happens in a chemical reaction.
What does it mean for a chemical equation to be balanced? When can it be stated that chemical equations are balanced?
It means that the same number of atoms of each element is present on each side of the arrow. They are balanced when they satisfy the Law of Conservation of Mass.
How do we balance a chemical equation?
By putting appropriate numbers, called coefficients in front of the formulas.
Do balancing equations examples from booklet.
Do balancing equations examples from Worksheet 1.
What is a cation and an anion?
A cation is a positively charged ion (a metal) and an anion is a negatively charged ion (a non-metal).
What can the structure of a metal be described as? What is it called? What are the cations and delocalised electrons held together by?
It can be described as a layer of cations surrounded by a sea of delocalised electrons. This structure is known as the metallic model. They are held together by the electrostatic forces of attraction.
What does delocalised mean?
It means that they are not held rigorously, and are free to move throughout the lattice - they belong to the lattice as a whole.
What are the 6 properties of metals?
1. Metals are good conductors of electricity.
Delocalised electrons are free to move – if a source of electric current is attached, electrons flow from negative to positive.
2. Metals are good conductors of heat
. When delocalised electrons bump into each other and into ions, they transfer energy. When heated, the particles vibrate more rapidly.
3. Metals are lustrous (shiny).
Delocalised electrons reflect light.
4. Metals are malleable and ductile.
Layers of cations can be forced across each other – the delocalised electrons move to compensate for this and re-establish the electrostatic forces of attraction. Malleable – able to be beaten into a sheet.
Ductile – able to be drawn into a thread.
5. Metals have high melting and boiling temperatures
Large amounts of heat energy are required to overcome the strong electrostatic forces of attraction between the cations and the delocalised electrons.
6. Metals are generally dense
. The ions in the lattice are closely packed.
What is some of the evidence that a chemical reaction has occurred? What is the evidence of a new substance being formed?
• Permanent change in colour.
• Temperature change.
• Release of light.
• Formation of a gas (evident as bubbles).
• Formation as an odour.
• Formation of a precipitate.
Evidence of a new substance being formed:
• Formation of a gas (evident as bubbles).
• Formation as an odour.
• Formation of a precipitate.
When are covalent compounds formed? What are they? How many do you form?
When non-metals are chemically combined. Each atom shares its electrons with others. These shared electrons form the 'glue' (covalent bond) that holds the atoms together. They are generally very strong. The amount of electrons that you share is how many covalent bonds you have (stops at 4 - because then they would be metals which aren't involved in covalent bonding).
What are some of the properties of covalent compounds?
• They are usually liquids or gases at room temperature.
• Have low melting and boiling points.
• Do not conduct electricity and heat.
Covalent bonds can form between a small number of atoms, a large number of atoms and an infinite number of atoms. What does each form?
Small - forms small molecules such as carbon dioxide (CO2).
Large - forms giant molecules such as plastics.
Infinite - forms giant lattices such as graphite, diamond and glass.
Draw Lewis diagrams and valance structures from booklet.
What types of elements exist as single atoms?
The Noble Gases. Examples: He, Ne, Ar Xe.
What non-metals exist as pairs of atoms?
H2, F2, Cl2, Br2, I2, N2.
What is the difference between names such as carbon monoxide, carbon dioxide, sulfur trioxide and dinitrogen tetroxide?
They indicate the number of atoms of each element in the molecules.
What is another name for hydrochloric acid?
What are molecular substances?
Molecular substances consist of seperate molecules containing a fixed number of atoms of each element. The names of the non-metal do not indicate the number of atoms in each molecule.
How many elements do metals consist of? How are they different do molecular substances?
They only consist of one element. The formula is the symbol of the element.
Fill out the ionic compounds on page 13 of booklet.
In order to conduct electricity, a substance must have what? What does this say about whether the substance is metallic, ionic and covalent?
A substance must have free moving charged particles. This shows that it is metallic if it is able to conduct electricity, as this is the only form of bonding where the particles are free to move around.
Answer the following questions relating to metallic, ionic and covalent.
- Particles in structure.
- Melting and boiling points.
- Conducts electricity when solid?
- Conducts when liquid (molten)?
- Conducts when dissolved in water?
- Cations and delocalised electrons.
- Generally high.
- Generally hard, but varies.
- Cations and anions.
- Yes (if soluble).
- Generally low.
- Generally soft.
- No (if soluble).
What are the four state symbols, and what for?
- Solid (s): solid, powder, pellets, metal, ribbon, turnings, precipitate.
- Liquid (l): liquid, molten, concentrated.
- Gas (g): gas, steam, vapour.
- Aqueous (aq): aqueous, dilute, solution, acids.
Write the chemical equations from page 15 and 16.
Give the formulas for the following:
- Hydrochloric acid.
- Nitric acid:
- Sulfuric acid:
- Carbon dioxide:
- Chlorine (gas):
- Nitrogen (gas):
- Oxygen (gas):
- Fluorine (gas):
- Carbon dioxide (gas):
- Carbon monoxide (gas):
- Hydrogen (gas):
- Phosphoric acid:
- Acetic acid:
- Carbonic acid:
Do worksheet 2.
What are combination reactions?
They are also known as synthesis reactions. This is when two or more chemical substances combine together to form a new chemical product.
What are decomposition reactions?
This is when on reacting substance forms several products.
What are precipitation reactions? How can a precipitate be removed? What are spectator ions?
They are also known as double displacement reactions. This is when two solutions containing dissolved ions (ironic solution) were mixed together, an insoluble compound sometimes forms. This insoluble compound, often as a solid, separates from the solution and is called a precipitate. Because the precipitate is insoluble, it can be filtered to be separated from the solution. Spectator ions are the ions that do not form a precipitate that are left free in the solution.
What does insoluble mean? What does soluble mean?
Soluble means that the ions dissolve in water. Ionic compounds that do not dissolve in water are called insoluble.
Do the examples from page 5 of booklet.
What is a dissociation reaction? How can you write dissociation equations?
Dissociation in chemistry and biochemistry is a general process in which molecules (or ionic compounds such as salts, or complexes) separate or split into smaller particles such as atoms, ions or radicals, usually in a reversible manner. When you write a dissociation reaction you separate the two ions, place their charges above their symbols, and then balance the entire equation.
What is a combustion reaction?
A combustion reaction occurs when a chemical substance burns in the presence of oxygen. This type of reaction produces energy that is felt as either heat (thermal) energy, light energy or sound energy. A reaction that produces energy is called an exothermic reaction.
What is complete combustion?
When the products of a combustion reaction with plentiful oxygen are carbon dioxide and water.
What is a redox reaction? Give an example of a redox reaction.
In many chemical reactions, electrons are either completely or partially moved from one atom, ion or molecule to another. This process is known as electron transfer. Chemical reactions that involve electron transfer are called redox reactions. An example of a redox reaction is a corrosion reaction, which is where a metal is 'eaten away' by substances in the air or water. One example of this is rust.
Which are two ways in which our environment can be protected from corrosion.
Galvanising: Galvanising metals occurs in roof construction, where a layer of zinc (a more reactive meal than iron) is coated on iron metal so that it will react with oxygen rather than the iron metal.
Protective paint: This protects the structure from corrosion.
What type of reaction is the example between an acid and a metal? What are its products?
The reaction between an acid and a metal is also an example of a redox reaction. The products of this reaction are a salt (ionic compound) and hydrogen gas. We can test for hydrogen gas with the pop test.
What are the three types of neutralisation reactions?
1. When an acid reacts with a metal hydroxide, a salt and water are produced.
2. When an acid reacts with a metal carbonate, a salt, carbon dioxide and water are produced.
3. When an acid reacts with a metal oxide, a salt and water are produced.
Write balanced equations using formulae for the following reactions.
(a) Aluminium metal + oxygen gas -> solid aluminium oxide
(b) Potassium metal + oxygen gas -> solid potassium oxide
(c) Solid carbon + oxygen gas -> carbon dioxide gas
(d) Solid copper carbonate -> solid copper oxide + carbon dioxide gas
(e) Iron metal + sulfur powder (S8) -> solid iron sulfide (FeS2)
(f) Copper sulfate solution + zinc metal -> copper metal + zinc sulfate solution
(g) Copper (II) sulfate solution + sodium hydroxide solution -> solid copper (II) hydroxide + sodium sulfate solution
(h) Solid magnesium hydroxide + hydrochloric acid -> magnesium chloride + water
State the reaction type(displacement,combination, decomposition, precipitation, combustion or neutralisation) for each of these reactions.
What are metal (single) displacement reactions?
When one element is removed, and it is replaced with another. In other words they swap partners.
Explain what a catalyst does and give three examples.
A catalyst is a way to increase the rate of a reaction. They are not changed by the reaction, nor do they change the reaction themselves. They work by helping bonds to break more easily, therefore, the reactants need less energy to react, and the reaction is faster. Three examples: Cars have catalytic converters, contact lenses are cleaned using a catalyst, and they are also in foods.
Why are catalysts important to industry?
They are important in an industry, as it allows a reaction to take place much more quickly, and therefore the result is known sooner. It allows the industry to make the most of their time and not waste it.
What are enzymes?
Enzymes are biological catalysts that exist within our bodies. They are large protein molecules and are essential for digesting food, breaking down toxic waste products and numbers other chemical processes that keep you alive and healthy.
Why do catalytic converters have a honeycombed surface?
Catalytic converters usually have a honeycomb shape to increase the surface area for reaction with the gases. The catalysts are platinum, rhodium and aluminium oxide.
Give one reason why the enzyme amylase is added to bread.
Because it is involved in the breakdown of starch into sugar.
What is the rate of a chemical reaction?
It is a measure of how quickly that reaction takes place. It doesn't change the amount of product that is formed - just how quickly it gets there.
What must happen for a chemical reaction to occur? What is this theory called?
For a chemical reaction to occur, the reactant particles must collide with enough energy as well as the correct orientation. This is called the collision theory.
Describe what happens when the reactant particles collide more frequently, and with greater proportions of collisions with enough energy.
The greater the rate of the reaction.
How can you ensure the rate of a reaction?
By the rate at which a reaction is used up, or the rate at which a product is formed.
Name some ways that you can speed up the rate of a reaction.
- Temperature - changing it, heating or cooling.
- Concentrating the solution.
- Increasing the surface area.
- Applying more pressure.
- Using a catalyst.
What does an increase in temperature do to the rate of a reaction?
It makes the particles in the reactant move faster and collide more often. This helps to speed up the reaction.
What is the concentration of a solution? What does it do to the rate of a reaction?
The concentration of a solution is a measure of how much substance is dissolved in water. If more of the substance is present, the more particles there will be. If there are more particles in the same volume, there is a greater chance that the particles will collide more often and the reaction will occur faster.
What do the size of particle do to the rate of a reaction?
Smaller particles have a greater overall surface area compared to larger particles. The greater the surface area, the easier it is for particles to react.
What does increasing the pressure do to the rate of a reaction? How can it be done.
Increasing the pressure, by decreasing the volume, of a reaction involving gases forces the gas particles closer together. This will increase the frequency of particle collisions, and therefore increase the rate of reaction.
What is a catalyst? What does using a catalyst do to the rate of a reaction?
Catalysts are not changed by the reaction. There is always as much catalyst present at the end of a reaction as there was at the start. Catalysts work by helping bonds to break more easily; therefore, the reactants need less energy to react and the reaction is faster. A catalyst can be recovered and used again and again. An enzyme is a special type of catalyst found in living things.
Do questions of page 11.