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science gcse revision, topic c6- the rate and extent of chemical change-,…
science gcse revision
topic b1
organisms can be
topic c6- the rate and extent of chemical change-
in chemistry the rate of making chemicals means the rate you make money.
the rate of chemical reactions is how fast the reactants are changed into products.
one of the slowest reactions is the rusting of iron.
other slow reactions- chemical weathering like acid rain damage to limestone buildings.
an example of a moderate pace reaction is metal magnesium reacting with acid to create a gentle stream of bubbles.
burning is a fast reaction but explosions are even faster and release a lot of gas.
you can find the speed of a reaction by recording the amount of product formed or the amount of reaction used over time.
the steeper the line on a graph the faster the rate of reaction
the rate of a chemical reaction depends on how often the particles collide(the collision frequency) the more collisions the faster the reaction, the energy transferred during a collision
the rate of reaction depends on- temperature, concentration of a solution or the pressure of gas, surface area and the presence of catalyst.
when the temperature increases so does the rate, if they are moving faster they're going to collide more frequently and the faster they move the more energy they have so more of the collisions will have enough energy to make the reaction happen.
increasing surface area increases rate- if one of the reactants is a solid then breaking it up into smaller pieces will increase its surface area to volume ratio this means that for the same volume of a solid the particles around will hae more area to work on so there will be collisions more frequently.
using a catalyst will increase the rate of a reaction-a catalyst is a substance that speeds up a reaction without being used up this means its not part of the overall reaction equation
different catalyst are needed for different reactions but they all work b decreasing the activation energy needed for the reaction to occur
chemistry 1 - atomic structure and the periodic table
atoms have a radius of 0.1 nano metres
the nucleus is the middle of the atom, it contains the protons and neutrons, it has a positive charge because of the protons, almost the whole mass of the atom is concentrated in the nucleus.
the electrons- they move around the nucleus in the electron shells, they're negativity charged but they cover a lot of space, the volume of their orbit determines the size of the atom and they have no mass.
protons- heavy and positive charge neutrons- heavy and neutral electrons-tiny and negatively charged.
atoms are neutral they have no overall charge unlike ions, this is because they have the same number of protons as electrons. in an ion the number of protons doesn't equal the number of electrons this means it has overall charge. e.g. an ion with a 2-charge has two more electrons than protons
the nuclear symbol of an atom tells you its atomic number and mass number. the atomic number tells you how many protons there are. the mass number tells you the total number of protons and neutrons in the atom. atomic number-mass number=no of neutrons.
its the number of protons in the nucleus that decides what atom it is. e.g. an atom with one proton in its nucleus is hydrogen and an atom with two protons is helium
if a substance only contains atoms with the same number of protons its called an element there are about 100 different elements.
atoms can be represented by symbols e.g. c=carbon, o=oxygen mg= magnesium Na=sodium Fe=iron Pb= lead
isotopes are different forms of the same element which have the same number of protons but a different number of neutrons. so isotopes have the same atomic number but different mass numbers.popular example of isotopes are carbon 12 and carbon 13.
topic p4- atomic structure
a Greek guy called Democritus thought that all matter was made up of identical lumps called atomos.
nearly 100 years later jj Thomson discovered particles called electrons that could be removed form atoms Thomson suggested atoms where spheres of positive charge with negative electrons stuck in them like fruit in the plum pudding model however in 1909 scientists in Rutherford lab tired firing a beam of alpha particles at thin gold foil this was called the alpha scattering method.
in 1804 john Dalton agreed with Democritus that matter was made up of tiny spheres that couldn't be broken up but he thought each element was made up of a different type of atoms .
because few alpha particles bounced back during the experiment the scientists realized that most of the mass of the atom must be concentrated at the center in a tiny nucleus, this nucleus must also have a positive charge since it repelled the positive alpha particles.
the nuclear model that resulted from the alpha particle scattering experiment was a positively charged nucleus surrounded by a cloud of negative electrons
about 20 years after the idea of nucleus was accepted in 1932 James Chadwick proved the existence of the neutron.
the nucleus is tiny but makes up most of the mass of the atom. it contains protons(positively charged) and neutrons (neutral) which gives it an overall positive charge
negative electrons travel around the nucleus really fast. the radius of an atoms is about 1x10 to the power of -10.m
electrons in energy levels can move within the atom and if they gain energy they move to a higher energy level, further away from the nucleus.
if one or more of the outer electrons leaves the atom, the atom becomes positively charged