Q4 Mod 3 Science test

• Chemical change is caused by chemical reactions.
• Chemical reactions are observed with the combination of the 5 evidences.
• 1. Production of light
  2. Temperature change
  3. Evolution of gas
  4. Formation of precipitate
  5. Change in intrinsic properties


  What are the five evidences
• Fire was the greatest discovery of all time. Theearliest people considered it as one of theearliest elements
• George Ernst Stahl stated that when a material burns, it releases a substance known as phlogiston and he called it the Phlogiston Theory.
• Antoine Lavoisier contradicts this theory as he carefully observed in his experiment that instead of releasing a substance, the material being burned reacts with oxygen. This is now known as the Theory of Oxidation, and this is accepted up to this day.
• 1. Oxygen
  2. Heat
  3. Fuel


  There are 3 factors that should be present in proper conditions and proportions for burning to occur:
• Chemical equation shows the symbols or formulas of the reactants and products, the phases (solid, liquid, gas) of these substances, and the ratio of the substances as they react
• 1. Shows a combination
  2. To produce
  3. Reversible action
  4. Heat is applied
  5. Its use as a catalyst or solvent
  6. Solid, liquid ,gas, aqueous

  
• Different types of chemical reactions

  1. Combination or synthesis
  2. Combustion
  3. Decomposition
  4. Single displacement
  5. Double displacement
  6. Acid base
• Combination


  A reaction when 2 or more reactants combine to form a single product
• Decomposition


  A single reactant breaks down into simpler ones. This is the reverse of the combination reaction. A catalyst, which may be in form of heat, electricity. radiation, or even enzyme, can aid or bring about a decomposition reaction.
• Single displacement 


  One element replaces another element from a compound. The more active element takes the place of the less active element in a compound.
• 
  

  The reactivity series also called the activity series ranks elements in order of their reactivity for certain types of reactions. including single replacement reactions. The more reactive elements will replace the less reactive elements in the reactivity series, but not the other way around. There are separate rankings for elements that form cations and elements that form anions
• Double displacement 


  This is when the positive ions (cations) and negative ions (anions) of different compounds switch places, forming two entirely different compounds
• Combustion


  This is when oxygen combines with a hydrocarbon (compound containing hydrogen and carbon) to form a water and carbon dioxide
• Acid base


  This is a special kind of double displacement reaction that takes place when anacid and base react with each other. The H+ of the acid reacts with the OH- ofthe base forming water and the other product is salt.
• All changes, whether chemical or physical, are accompanied by a change In energy. Some chemical reactions absorb energy: others release energy. Chemical reactions observe energy conservation, or the Law of Conservation of Mass and Energy.
• Any energy released in a reaction is presentin the chemical bonds of the reactants.There are numerous chemical reactions thatrelease energy. These types of reactions are called exothermic reaction
• Any energy absorbed in a reaction becomespart of the chemical bonds of the products.These types of reaction are less common. Endothermic reactions are chemicalreactions that absorbs energy.
• 
  

  A chemical equation describes what happens in a chemical reaction. Balancing a chemical equation refers to establishing the mathematical relationship between quantities of reactants and the products
• The Law of Conservation of Mass and Energy was tested by Antoine Lavoisier in the 17th Century. Lavoisier did his experiments on combustion and oxygen. He found out that the oxygen is the most essential element for a combustion reaction. He also found out that during combustion, the mass is conserved.
• Based on Collision Theory, not all collisions between the molecules result in the formation of products. Effective collisions between molecules only occur when two conditions are met:
• The colliding molecules should possess a minimum kinetic energy, known as activation energy.
• The reactant molecules should be in correct orientation when they collide.
• 
  

  When molecules collide. a certainminimum energy called activation energy is required for a reaction tooccur. This was suggested in 1888 by Svante Arrhenius. Activation energy isneeded to break the bonds of thereactants to form new products orsubstances.
• 1. Particle size
  2. Temperature
  3. Concentration
  4. Catalyst


  What are the factors affecting chemical reactions
• Particle size 


  When reactants are present in small pieces, reaction rates can increase. The smaller pieces have a greater surface area thus. providing much greater contact among the reactants and effecting more collisions
• Concentration 


  the measure of the numberof particles of solute contained in each volume of solution. The greater the number ofparticles, the greater the collision. When thereare a great number of particles, therehigh concentration leading to greaterchances of collision. Thus, a reaction will occur.
• Temperature 


  Increasing the temperature increases the rate of reaction. Therefore, heating allows more frequent collisions among particles. Most frequent collisions will lead to sufficient energy that will provide necessary activation energy for the reaction to start
• Catalyst


  The rate of chemical reactions can be altered. The substance that alters the rate or speed ofchemical reactions is called a catalystGenerally, a catalyst is used to speed upchemical reaction but there are also catalyststhat slows down a reaction. These are known as inhibitors.
• Catalyst


  alters the speed of reaction by changing the activation energy. The figure shows a diagram how the enzyme that acts as the catalyst speeds up a chemical reaction works by decreasing the activation energy