Week 8/9 Flashcards
What does the occurrence of temperature change indicate?
That energy has changed form
What evidence will chemical change usually produce?
A gas produced A precipitate is formed A permanent colour change An apparent change in mass A temperature change
What may be needed for a reaction to occur or what may be produced as a result of the reaction?
Energy
What happens to the bonds when a reactions occurs?
Some bonds are broken and some are formed.
If less energy is stored in the products then was present in the reactants, then what happens?
The surplus energy is released as heat.
What do all molecules contain? Where is it contained?
Stored chemical energy
Contained within the bonds that are between the atoms that are within the molecules and within the the bonding between the molecules themselves.
What is the stored chemical energy called and what is its symbol?
Enthalpy or heat content
H
Formula for the change in enthalpy?
△H = H products - H reactants
*△H = change in enthalpy
What happens in an endothermic reaction?
△H is +
E products > E reactants
Heat energy added to the reactants (absorbed)
What happens in exothermic reactions?
△H is -
E reactants > E products
Heat energy released by reactants
What will often happens to the surrounding temperature during an exothermic reaction?
It increases
Eg of endothermic reactions?
Photosynthesis, evaporation of water, backing bread
Eg of exothermic reactions?
Lighting Bunsen burner, rust, formation of snow in clouds
Define redox reaction?
A chemical reaction that involves the transfer of electrons either by gaining or losing them
What is involved in oxidation?
Gain of oxygen
Loss of hydrogen
LOSS OF ELECTRONS
What is involved in reduction?
Loss of oxygen
Gain of hydrogen
GAIN OF ELECTRONS
Acronym for oxidation and reduction?
OIL RIG
Oxidation Is Loss Reduction Is Gain
Define the reactivity/activity series?
Ranks metals on their desire to lose electrons
The MORE reactive element wants to form IONS
K wants to lose electrons
Au wants to lose electrons
Define soluble?
A substance that is able to be dissolved, especially in water
Define insoluble?
A substance that is unable to be dissolved
Define precipitate?
When a substance is deposited in solid form from a solution
Define ionic compound?
A chemical compound that is held together by electrostatic forces called ionic bonds
Define cation?
Positively charged ions
Define anion?
Negatively charged ions
Describe what happens when a substance dissolves?
The substance will begin to break down into its molecules once in the liquid.
It will separate into its ions which are not able to be seen by the naked eye.
Define monatomic?
Consisting of one atom
Define polyatomic?
Consisting of two or more atoms
Define combustion?
Rapid chemical combination of a substance with oxygen, involving the production of heat and light.
Define rate of reaction?
The speed at which a chemical reaction proceeds
List the five ways that the rate of a chemical reaction can be controlled?
Temperature Concentration Agitation Surface area Catalyst
Effect of temperature on the rate of a chemical reaction?
Increasing the temperature will normally increase the rate of the reaction
Effect of concentration on the rate of a chemical reaction?
Increasing the concentration of the reactants will increase the rate of the reaction.
Effect of surface area of reactants on the rate of a chemical reaction?
If the reactants is crushed up the rate of reaction will increase
Effect of catalysts on the rate of a chemical reaction?
If a catalyst is added then the reaction rate will be sped up
Describe what enzymes do?
They hold reactants molecules together until they rearrange to form products. Eg amylase
Why are enzymes so important in digestion?
They break down the starches and complex carbohydrates into simple sugars for easy absorption into the body
