- Stoichiometry is used to measure the total amount of substances in a chemical reaction
- it relates to the law of conservation of mass and the law of definite proportions
- used to determine the amount of reactant and product in the chemical reaction
- when using stoichiometry a balanced equation is needed in order to calculate the correct answer
ex 1. With 27.1g of calcium oxide, what is the amount of moles of calcium oxide.
27.1g CaO*(1 mol CaO/56.08g CaO)= 0.484 mol CaO
ex 2. What is the total amount of sodium hydroxide that is needed to make 250 ml of 0.200M solution, in grams.
Lab 5B is the first lab we did which dealing with reaction this term. There are totally seven reactions including Sythesis, Single Replacement, Decomposition and Double Replacement. The objective of this lab is to observe a varity of chemical reactions and to classify each reaction as one of the four main types.
(Several chemical reagents have been used in this lab, so wearing a safety goggle and lab apron is necessary. )
Reaction 1 (2 Cu + O2 = 2 CuO)is a sythesis reaction, though it need high temperature to achieve the reaction. In that case, you will find red copper wire become dark black at last.
Reaction 2 (2 Fe +3 CuSO4 = Fe2(SO4)3 + 3Cu) is a Single Replacement, which using Fe to replace Cu. We put a iron nail into blue solution which is CuSO4. Several seconds later, some rust appears and the shiny iron nail becomes black.
Reaction 7 (2 H2O2 + (MnO2) = 2 H2O + O2). This one is quite different from before, in that case, MnO2 is a kind of catalyzer which will not avolved in the reaction. So as you see in right hand side, the products, there is even no element Mn. However, this catalyzer is quite good, the reaction will be very fast with only a little MnO2.
This lab shows some basic reactions in daily chemistry. Some reactions are very familiar in our everyday life. For example, reaction 3(CuSO4*5H2O = CuSO4 + 5 H2O) is the most common way to make pure CuSO4 in industry.
Balancing equation is like a math work. It is depended on The law of conservation of mass. So that, the mass of reactants = the mass of products.
When balancing a equation, first you have to count the number of atoms of each elements.
For example, H2+O2=H2O, there are 2 H and 2 O in left hand side and there are 2 H and 1 O in right hand side. That means H:O=2:1. So for reactants H:O should be 2:1 too. So there should be 4H and 2O in right hand side and left hand side. Finally, we get 2H2+2O2=2H2O....
For some other types of reactions like single replacement, you can use a easier way to balance equation. For example, Fe + CuSO4 = Cu + Fe2(SO4)3. In that case, (SO4)2- can be seen as a whole. So you can find there are 2 (SO4)2- in right hand side. Than you can guess 3 CuSO4 in left hand side, that means there should be 3 Cu in right hand side. At last, obviously, 2 Fe in both right and left hand side. Finally the equation should be 2 Fe + 3 CuSO4 = 3 Cu + Fe2(SO3)2.
That is a my own way to balance equation. You may find a Better way when doing more exercise. Many convinience strategy will be found when you get more experience in balancing equation.
Chemical reactions can be classified as one of six main types: synthesis, decomposition, single replacement, double replacement, neutralization, combustion.
SYNTHESIS: A synthesis reaction is when two or more simple compounds combine to form a more complicated one.
element+element--compound A+B --AB Eg: hydrogen + oxygen -- water
DECOMPOSITION: A decomposition reaction is the opposite of a synthesis reaction - a complex molecule breaks down to make simpler ones compound--element+element AB--A+B Eg: calcium chlorate-- calcium chloride + oxygen
SINGLE REPLACEMENT: This is whenone element trades places with another element in a compound.
element+compound --element + compound A+BC--B+AC [A=metal] A+BC--C+BA [A= non metal] Eg aluminum+ lead nitrate--aluminum nitrate +lead
DOUBLE REPLACEMENT :This is when the anions and cations of two different molecules switch places, forming two entirely different compounds
NEUTRALIZATION :This is a special kind of double displacement reaction that takes place when an acid and base react with each other. acid+ base--salt+water HA+BOH---AB +H2O Eg; sulphuric acid + sodium hydroxide--sodium sulphate +water
COMBUSTION: A combustion reaction is when oxygen combines with another compound to form water and carbon dioxide. Eg: hydrocarbon+ oxygen --carbon dioxide +water
2012年2月8日星期三
-energy absorption and reduction may be laced in the equation -exothermic reaction have the Right hand side energy term and is usually a negative ΔH -endothermic reaction have the left hand side energy term and is usually a positive ΔH - ΔH=energy change of reaction and expressed in kJ/mol of one of the chemical Eg. 2Ba+O2→2BaO+1115kJ for this equation the exothermic reaction would be 557.5kJ/1mol Ba or 1115kJ/2mol O2 -ΔH value depends on which chemical is used in the equation -molar mass is different for each chemical reaction, so is the ΔH for different chemical reaction 2Ba+O2→2BaO+1115kJ -1500kJ*-1molBa/1115kJ= 1.345mol Ba= 1.3mol Ba Example 1:
