USING ENGLISH TO PREDICT RENDEMENT OF PRODUCT A REACTION

How to Predict Products in Chemical Reactions

 Predicting Products of Chemical Reactions

This worksheet is designed to help you predict products of simple reactions of the four basic reaction types (synthesis, decomposition, single replacement, and double replacement) and combustion reactions.

For the first few reactions, the type of reaction is listed, you should predict the products, then balance. Further questions just have the reactants listed and you should decide on the type of reaction, as well as the correct products. Many of these reactions fall into the category of redox reactions, though do not let that confuse you...each can be described in terms of the four basic reaction types (except the combustion reactions).

Although states (s, l, g, aq) of the reactants and products are very important in a chemical reaction, don’t worry about determining those for these problems. Rather, focus on what products might result from the reactants given. Pay particular attention to the ionic charge of species that you know form ions with only one possible charge (e.g., alkali metals, alkaline earth metals, halogens, etc.)

For all combustion reactions of hydrocarbons or hydrogen-carbon-oxygen molecules, the products will always be CO2 and H2O (assuming a complete reaction).

a. Combustion: C6H12 + 9O2 → 6CO2 + 6H2O

b. Combustion: 2C4H6 + 11O2 → 8CO2 + 6H2O

c. Combustion: C6H10O3 + 7O2 → 6CO2 + 5H2O

1. Synthesis: Mg + I2 → MgI2

Note that Mg can only form Mg2+ and I can only form I-, so the product will must have a 1:2 cation : anion ratio.

2. Double displacement: CuCl2 + H2S → CuS + 2HCl

Note that the product is not H2Cl2. It is important to recognize that CuCl2 is made of three ions, Cu2+ and two Cl-.

3. Double displacement: NaOH + HClO4 → NaClO4 + H2O

In this question, you must recognize that perchlorate, ClO4-, and hydroxide, OH-, are polyatomic ions and will not break apart. Also, this is an acid-base reaction, so the products should be salt and water.

4. Decomposition: ZnCO3 + heat → ZnO + CO2

When reactions have heat as a reactant, it is very likely that they will involve decompositions. Carbonate compounds usually decompose to CO2 and a metal oxide.

5. Single replacement: 2HCl + Zn → ZnCl2 + H2

Note that one reactant is in its elemental form; if a single replacement reaction is going to occur, the species NOT in its elemental form in the reactants (H+ in this case), will end up in its elemental form in the products (H2) and the species that IS in its elemental form (Zn) will end up ionized (Zn2+). Note that zinc can only form a Zn2+ ion, so it will have two chloride ions. Note also that hydrogen in its elemental form is H2, not H.

6. Single replacement 2Na + MgCl2 → 2NaCl + Mg

Again notice that one species is in its elemental form (Na). The magnesium in MgCl2 is an ion (Mg2+), but is transformed into its elemental state (Mg), while the Na is converted into an ion (Na+, sodium only forms a +1 ion).

7. Double replacement CaCl2 + K2CO3 → CaCO3 + 2KCl

Recognize that carbonate is a polyatomic ion (CO32-) and that the cations are already stable ions (Ca2+ and K+).

8. Synthesis 2K + Cl2 → 2KCl

Note that both materials are elemental species, so the only result could be a synthesis reaction. In the product, K+ and Cl- are formed. Note that we would NOT write the product as K2Cl2. Ionic compounds are written in their simplest forms.

9. Double replacement 3BaCl2 + 2K3PO4 → Ba3(PO4)2 + 6KCl

Note that phosphate (PO43-) is a polyatomic ion and will not break apart. Since barium is a +2 ion, the barium phosphate will have a 3:2 ratio of Ba:PO4 in order to balance the charge.

10. Double replacement H2SO4 + 2KOH → 2H2O + K2SO4

Notice that sulfate (SO42-) is a polyatomic ion and that potassium exists as a +1 ion (K+). Also, this is an acid-base reaction, so the products should be salt and water.

11. Decomposition Al2(CO3)3 + heat → Al2O3 + 3CO2

Another decomposition that will generate CO2 and a metal oxide (note that Al forms a +3 ion, Al3+, and monatomic oxygen will have a –2 charge, O2-).

12. Synthesis 4Al + 3O2 → 2Al2O3

Each species is in its elemental form, so a synthesis reaction is expected. Since the most stable ionic form of aluminum is Al3+ and oxygen is O2-, Al2O3 will form (positive and negative charges must cancel out). Note that the elemental oxygen (O2) is diatomic, but in the product, you no longer have elemental oxygen, since it is now an ion.

13. Double replacement Pb(NO3)2 + 2KOH → Pb(OH)2 + 2KNO3

Note that there are two polyatomic ions present in the question: nitrate (NO3-) and hydroxide (OH-). The lead has a +2 charge so it will require two negative ions to make a neutral salt (Pb(OH)2). Note that potassium only has a +1 charge (K+), so when it forms a compound with nitrate, it must occur with a 1:1 ratio (KNO3).

14. Double replacement H2SO4 + BaCl2 → BaSO4 + 2HCl

Notice that the BaCl2 is made of three ions (Ba2+ and two Cl-). BaCl2 does not represent a barium ion and elemental chlorine. As a result, the chlorine in the product will not be Cl2.

15. Single replacement Ca + 2AgCl → CaCl2 + 2Ag

With one species in its elemental form (Ca), this will be a single replacement reaction. Note that calcium can only form a +2 ion (Ca2+) and that the chlorine can only have a –1 charge (Cl-), so the salt produced must be CaCl2.

16. Double replacement H3PO4 + FeBr3 → FePO4 + 3HBr

Note that phosphate has a –3 charge (PO43-) and that the iron has a +3 charge (Fe3+).

17. Synthesis 6Li + N2 → 2Li3N

Recall that the monatomic charge for lithium is +1 (Li+) and nitrogen is –3 (N3-). To form a neutral compound, there must be three +1 charges to match the one –3 charge.

18. Double replacement 2HCl + Mg(OH)2 → MgCl2 + 2H2O

This one should have been easy by now.... (Plus, this is an acid-base reaction, so the products should be salt and water.)

19. Decomposition Mg(OH)2 + heat → MgO + H2O

Hydroxides will often decompose with heat to yield water and an oxide. When you get to the Chemistry of Copper lab, you will see a dramatic change involving copper(II) hydroxide becoming copper(II) oxide.

20. Decomposition 2Fe(OH)3 + heat → Fe2O3 + 3H2O

Similar to the question above. Notice that the metal retains its ionic charge, it is Fe3+ in both the reactants and products.

Predicting Reaction Products

When cooking, it's frequently handy to predict what will happen when we mix a bunch of ingredients together. For example, if we're interested in making a delicious new salad dressing, we would have a very small chance of making anything edible if we had no way of knowing which ingredients would have the greatest chance of succeeding. Likewise, it's often necessary for chemists to predict the chemical reactions that will take place when two chemicals are combined. For example, if we're adding a chemical to a tank of toxic waste to stabilize it, we'd be very unhappy if we failed to predict an explosive reaction. An easy way to predict what reaction will take place when two chemicals are mixed is to identify the type of reaction that's likely to occur when the chemicals are combined. Of course, we mentioned before that these types of reaction are arbitrary, but they do sometimes have a useful purpose.

Here are some tips you may find handy in helping to predict the type of reaction that will occur if you know only the reactants. Keep in mind that not all combiations of chemicals will result in a chemical reaction—these tips are handy only for helping to predict what would happen should they happen to react.

• If two ionic compounds are combined, it's usually safe to predict that a double displacement reaction will occur.
• If the chemicals mixed are oxygen and something containing carbon, it's usually a combustion reaction.
• If we start with only one reactant, the reaction taking place is probably a decomposition reaction. To predict the products of such a reaction, see what happens if the chemical breaks into smaller, familiar products such as water, carbon dioxide, or any of the gaseous elements.
• When pure elements are combined, synthesis reactions are the frequent result.
• If a pure element combines with an ionic compound, a single displacement reaction may take place.
• If a compound containing the hydroxide ion is involved, check the other compound to see if it contains hydrogen. If it does, it may be an acid-base reaction.

PREDICTING PRODUCT OF CHEMICAL REACTIONS

Type Of Reactions	Reactants	Probable Products	Generic Equation
Synthesis	Two or more substances	One compound	A+ B → AB
Combustion	√ a metal and oxygen    √ a nonmetal and    oxygen                          √ a compound and oxygen	√ the oxide of the metal          √ the oxide of the nonmetal                                  √two or more oxsides	A + O2 → AO
Decomposition	One compound	Two or more elements and/or compounds	AB→ A+ B
Single- replacement	√ a metal and a compound                     √ a nonmetal and a compound	√ a new compound and the replace metal    √ a new compound and replace nonmetal	A + BX → AX + B
Double-replacement	Two compounds	Two different compounds, one of which is a solid, water, or gas	AX + BY → AY + BX

SOURCE : https://www.infoplease.com/science/chemistry/chemistry-predicting-reaction-products
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