Pops, Potions, Poisons

1.        Physical & Chemical Change

• physical changes can make substances appear differently

• a physical change happens when matter changes size, shape or form.

• Physical change can also be the change of one state of matter to another.

• e.g. changes in shape or form, mixing, dissolving a solute, expansion, compression

• a chemical change has occurred when the substances that make up an object have been changed into other substances.

• You can’t always see chemical reactions

• chemical changes involve changes to the chemical inside a substance. this can happen through making new molecules, new compounds, or just rearranging the atoms to be structured differently.

• the final substance has to be chemically different to the starting substances to make a chemical change.

• they cannot be reversed by physical means and often cannot be reversed at all.

• chemical changes are less obvious than physical changes

• look for the effects they have on other substances

• you can’t observe them directly - microscopic.

• colour change, substances disappearing, new substances appearing, bubbling or gas, temperature changes and sound/light are all indicators of chemical change

Chemical

·        a chemical change has occurred when the substances that make up an object have been changed into other substances.

·        You can’t always see chemical reactions.

·        Involve changes to the chemical inside a substance

·        Can happen when:\

-            Making new molecules

-            Making new compounds

-            Rearranging atoms to be structured differently

·        Make substances actually different

·        The final substance has to be chemically different to the starting substances

·        Can’t be reversed by physical means and often cannot be reversed at all.

·        Indicators:

-            Can’t be observed directly – microscopic

-            Look for effects they have on other substances

-            Less obvious

-            Colour change

-            Substances disappearing

-            New substances appearing

-            Bubbling and gas

-            Temperature changes (of reactants)

-            Sound & light

Synthesis and Decomposition

Decomposition:

·        Decomposition is when a compound breaks down into simpler parts – smaller compounds or elements

·        Occur when a single reactant breaks apart to form multiple products

·        Requires energy either in the form of heat or electricity

·        The absorbed energy causes the reacting substance to break down.

·        Compounds decompose but elements cannot!

·        AB à A+B

·        Example: passing electricity through water – heats water up, giving off oxygen and hydrogen gases.

Synthesis

·        Occur when multiple reactants combine to form a single product

·        A+Bà AB

·        Two elements reacting to make a compound

2.        Exothermic and Endothermic Reactions

·        Chemical reactions involve energy transfer.

Endothermic:

·        When energy is absorbed by a reaction, it is called endothermic.

·        Endothermic reactions take energy away from their surroundings and feel cold as a result.

·        Example: Photosynthesis in leaves is a reaction powered by sunlight. It is an endothermic reaction because the energy from sunlight is absorbed to power the reaction.

Exothermic:

·        When energy is released by a reaction, we call is exothermic

·        Exothermic reactions release energy into their surroundings and feel hot as a result.

·        Example: fires are reactions that release huge amounts of heat. They are exothermic reactions because they release energy into the air around them.

3.        Reaction Rates

·        The term ‘rate of reaction’ refers to the speed at which a reaction occurs. i.e. how fast products are created and reactants are used up.

·        You can get an indication of the rate of reaction by approximately measuring how fast one or more products are made, or how fast one or more reactants are used up.

·        Reactions happen when particles interact – specifically when they collide.

·        The time it takes for the reactants to fully react and turn into products depend on how many collisions occur every second.

·        If there aren’t many collisions, the reaction will be slow. If there are a lot, the reaction will be fast.

·        If we want to change the rate of reaction. We can change either how many collisions occur or how effective the collisions are.

·        Factors that control the rate of reaction:

-            Temperature

-            Concentration

-            Agitation

-            Surface area

-            Catalyst

4.        Effect of factors (e.g. temperature + catalysts) on the rate of common chemical reactions explained using collision theory.

·        Collision Theory states that for a reaction to occur the reactant molecules must collide, and in order for this collision to result in product formation two things must occur:

-            The collision must have adequate kinetic energy to drive the reaction (activation energy) and the molecules must collide with the correct geometry to allow for a reaction to occur,

-            The rate of a reaction is a result of these factors, for example more collisions per second will lead to an increased rate.

·       

At higher temperatures more molecules will possess a higher kinetic energy and so the Maxwell-Boltzman distribution is shifted so that more collisions have energy or equal to the activation energy

·        A catalyst speeds up a chemical reaction, without being consumed by the reaction. It increases the reaction rate by lowering the activation energy for a reaction. (Activation energy is the minimum amount of energy required for a reaction to occur.

·        Because the activation energy is lowered, more reactant molecules will have enough energy to overcome the energy barrier and react, thus increasing rate of reaction.

·        Catalysts provide an alternative reaction pathway that requires less energy.

5.        Law of Conservation of Mass

·        The total mass of the reactants is always equal to the mass of the products when a reaction occurs in a closed system.

·        The law using the atomic theory: the atomic theory states that all matter is composed of atoms which, in chemical reactions, are simply re-arranged, and not created or destroyed.

6.        Basic laboratory equipment and functions

7.        Define the terms element, compound, mixture, atom, molecule and draw diagrammatic models to distinguish between the terms

·        Element

-            a substance that cannot be broken down into any other substance.

-            Every element is made up of its own type of atom.

-            Can’t be separated by physical means

-            Properties – state, colour, conductivity etc.

-            E.g. oxygen and copper

·        Compound

-            a substance composed of two or more different elements chemically combined.

-            Can’t be separated physically

-            Different types of atoms

-            Properties do not change regardless of how it is prepared.

·        Mixture

-            combination of two or more substances where each substance retains its own properties and is not chemically bonded to the others.

-            The substances in a mixture can be separated by physical methods such as filtration.

-            Arranged in homogeneous or heterogeneous mixtures

-            Properties don’t change

-            E.g. party mix

·        Atom – the smallest unit of a chemical element, the fundamental building block of matter. Retains the chemical properties of that elements. Consists of a nucleus surrounded by electrons.

·        Molecule – a group of two or more atoms chemically bonded together, forming the smallest unit of a substance that retains the chemical properties of that substance.

8.        Recall names and formula of some common compounds

·        Water = H₂O

·        Carbon dioxide = CO₂

·        Hydrochloric acid = HCl

·        Table salt = NaCl

·        Methane = CH4

9.        Outline the work of Mendeleev in the development of the modern periodic table

·        Mendeleev produced his periodic table in 1869 by arranging elements in order of increasing atomic weight and then grouping them based on their similar chemical properties.

·        He left gaps in his table for currently unknown elements that predicted their presence.

·        Elements are arranged by similarity of properties in both Mendeleev’s and the modern periodic table.

·        Mendeleev’s table was arranged by mass, but the modern table is arranged by atomic number.

10.   Distinguish between protons, neutrons and electrons using a knowledge of their properties and describe the basic structure of atoms.

11.   Describe the organisation of elements in the periodic table using their atomic number, electron arrangement and the concept that elements with similar properties fall into the same vertical groups.

·        Elements are organised in ascending order by number of protons (atomic number)

·        The number of electron shells an element has dictates the period or row it sits in in the periodic table. For example, if sodium has 3 shells it sits in the third period.

·        The number of electrons in the valence electron shell of an atom dictate which group the element sits in. For example, if sodium has 1 electron in its valence shell, we can infer that it belongs in group 1.

·        Elements with similar properties are grouped together because they share the same number of valence electrons. This similarity in valence electron configuration leads to similar chemical behaviours and reactivities.