- Flashcards
Distinguish chemical reactions from phase transitions and separation methods.
- A chemical reaction produces new substances and is irreversible.
E.g. : baking a cake. - A phase transition only changes the state of the substance, basically its appearance.
E.g : melting ice so it becomes a liquid. - A separation method separates a mixture, but does not form new substances.
E.g. : separating sand from water using a filter.
Explain the difference between compounds and elements at a micro level.
Imagine you take a water molecule, and try to decompose it. You’ll end up with two hydrogen atoms and one oxygen atom. These atoms will regroup to the atoms of the same type. But if you take a gold molecule and try to decompose it, you’ll just end up with only one type of atom.
Explain the structure of the periodic table of elements.
The 18 groups tell you which elements have similar properties (chemical reactivity).
The 7 periods tell you how many energy levels the elements’ atoms have (electrons on the outer shell).
Name all the metals you need to memorise (elements)
-Aluminium: Al (s)
-Sodium: Na (s)
-Calcium: Ca (s)
-Potassium: K (s)
-Copper: Cu (s)
-Iron: Fe (s)
-Lead: Pb (s)
-Magnesium: Mg (s)
-Zink: Zn (s)
Name all the non-metals you need to memorise (elements).
-Carbon: C (s)
-Sulphur: S (s)
-Hydrogen: H (g)
-Oxygen: O (g)
-Nitrogen: N (g)
-Fluorine: F (g)
-Chlorine: Cl (g)
-Bromine: Br (g)
-Iodine: I (g)
Explain the difference between mixtures and pure substances.
A mixture consists of multiple types of molecules, whereas a substance only of one type of molecule. You could separate a mixture physically (saltwater), but a pure substance cannot be separated physically (water).
Name the steps for balancing chemical equations.
- Start with metals. (Aluminium, Lead, fewer compounds).
- Balance non-metals (Carbon, Nitrogen, fewer compounds).
- Hydrogen.
- Oxygen.
- Eliminate fractions.
Why is ultraviolet radiation effective at causing photolysis?
Because UV rays have shorter wavelengths, and therefore carry more energy with them, and can break chemical bonds easily.
Why is the volume of hydrogen twice the volume of oxygen during the electrolysis of water?
Because of the formula: 2H2O = 2H2 + O2
What characteristics usually indicate that a decomposition reaction has taken place?
- Single reactant breaks down into two or more simpler products.
- Bubbles or gas have been released. (Formed one of the products).
- May change from solid to liquid, or from liquid to gas.
Why do you hear a bang when water is formed from hydrogen and oxygen?
Considering it’s a combustion reaction, the bang you hear is due to the rapid release of energy when hydrogen and oxygen combine.
Name the three types of decomposition reactions and the type of energy that is used.
- Thermolysis : decomposition by heating.
- Electrolysis : decomposition by supplying electrical energy.
- Photolysis : decomposition under the influence of radiant energy.
Rules for balancing chemical equations.
- The number of atoms stays the same before and after.
- Coefficient is a whole number.
- Coefficients as small as possible.
- Index must not be changed.
In what order are the elements in the periodic table of elements?
In the order of increasing atomic mass.
Name all the formulas that are required to calculate either the mass, density, or volume.
- p = m/v
- m = p x v
- V = m/p
Name the 4 groups you need to memorise and their properties.
- Alkali metals : highly reactive (with water).
- Alkaline earth metals : reactive, but less.
- Halogens : highly reactive (with metals, non-metals).
- Noble gases : very low reactivity.
Describe how CO2 dissolves in water and why it creates a sparkling effect.
CO2 is weakly soluble in water, but it does happen under high pressure and forms the carbonic acid. Because the gas has such a low density, it quickly rises upwards and creates bubbles.
Explain the decomposition reaction of silver chloride.
Silver chloride consists of two elements: silver (a solid), and chlorine (a gas). When silver chloride is left under sunlight, the light energy breaks the chemical bonds between these two elements. The chlorine gas escapes into the air, and the silver remains behind as grey particles.
What do you need for a combustion to happen?
- A flammable substance (fuel).
- (Sufficient) oxygen.
- A temperature above the ignition temperature.
What form of energy does a combustion release? And what phenomenon does it result in?
It releases energy in the form of heat, which results in a fire phenomena.
What reaction products do hydrocarbons produce in a complete combustion?
CO2 and H2O.
What reaction products do hydrocarbons produce in a incomplete combustion?
CO with H2O, or C with H2O.
What are the characteristics of an optimal reagent?
- It is selective: reacts with only one type of substance.
- It is sensitive: only a small amount of the substance is needed.
Explain how you can identify carbon dioxide with a reagent.
You can identify carbon dioxide with lime water. If the carbon dioxide passes through the lime water, the substance will turn from a colourless liquid to a cloudy, white liquid.
