chemical reactions

Question 1

chemical reactions

Answer 1

when particles collide and are rearranged to form new particles. chemical reactions involve energy changes.
as the reactant particles are rearranged, the chemical energy of the reactants is changed also.
energy can be absorbed or released

Question 2

chemical energy

Answer 2

stored in chemical bonds between atoms and molecules. energy results from:
attractions between electrons and protons
repulsion between nuclei
repulsion between electrons
movement of electrons
vibration and rotation around bonds

Question 3

law of conservation of energy

Answer 3

states energy cannot be created or destroyed.
chemical energy stored in a substance reduce and the energy must go elsewhere
a substance can’t gain in chemical energy without absorbing that energy from another source

Question 4

system

Answer 4

the chemical reaction

refers to energy changes that occur as bonds and formed between the atoms of the elements involved in the reaction

Question 5

surroundings

Answer 5

everything but the chemical reaction

energy goes from the surrounding to the reaction or energy is released into the surroundings

Question 6

energy changes

Answer 6

the reactants in a reaction have a certain amount of energy in bonds, since the products are a rearrangement of the particles so they have different bonds and thus different amount of energy
for particles to separate,

energy is required, the separated articles have more energy than when they were together. particles coming together the products will have less energy than the separate particles, this lost energy is transferred to the surroundings

Question 7

specific heat capacity

Answer 7

energy needed to change temperature of 1kg of a substance by 1 degree

Question 8

exothermic

Answer 8

energy of products is less than energy of reactants and the lost energy is transferred to its surroundings

Question 9

endothermic

Answer 9

when energy of the products is greater than the energy of the reactants
energy is absorbed from the surroundings

Question 10

melting/boiling

Answer 10

endothermic

Question 11

freezing

Answer 11

exothermic

Question 12

enthalpy

Answer 12

stored chemical energy of a substance

Question 13

activation energy

Answer 13

energy required to break the bonds of reactants so that a reaction can proceed
energy barrier that must be overcome before a reaction can start
unless this minimum energy amount is met, reactants rebound and move away from each other without reacting

Question 14

combustion

Answer 14

the release of chemical energy when the fuel is burnt in the presence of oxygen
exothermic

Question 15

complete combustion

Answer 15

when oxygen is plentiful and products are carbon dioxide and water

Question 16

incomplete combustion

Answer 16

when oxygen supply is limited

not all carbon can be converted into carbon dioxide so carbon monoxide and or carbon is produced instead

Question 17

energy content of fuels

Answer 17

heat of combustion of a fuel is defined as enthalpy change when a specified amount of fuel burns completely in oxygen
energy content: chemical energy available from a substance
fuels have high energy contents

Question 18

factors that affect reaction rates

Answer 18

surface area of solid reactants
concentration of reactants in a solution
gas pressure
Temperature 
presence of catalysts

Question 19

rate of reaction

Answer 19

change in concentration of a reactant or product per unit time
need to measure amount of product being formed or amount of reactants being used up in a given ti8me period
depends on activation energy
magnitude of activation energy determine how easy it is for a reaction to occur and what proportion of collisions result in a successful reaction

Question 20

collision theory

Answer 20

for collision theory to occur reactant particles must
collide with each other
collide with each other with sufficient energy to break bonds between the reactants
collide with the correct orientation to break the bonds between reactants and so allow formation of new products, if not correct orientation, particles bounce off each other

Question 21

transition state

Answer 21

a new arrangement of atoms when activation energy is absorbed
occurs at the stage of maximum potential energy in the reaction (activation energy)
bond breaking and forming occur at this stage and arrangement of atoms is unstable

Question 22

increase reaction rate

Answer 22

increasing a number of collisions that can occur in a given time
increasing proportion of collisions with an energy equal or greater than the activation energy

Question 23

increasing frequency of collisions

Answer 23

increasing concentration of reactants (increasing pressure increase concentration)
increasing surface area of a reactant (more particles, more exposed surfaces of particles )
increase pressure

Question 24

increasing energy of reactions

Answer 24

increasing temperature

catalyst lower activation energy required