balancing chemical equations, types of reactions, Predicting Chemical Products

Chemical Equations

A chemical reaction occurs when one or more substances combine or decompose to form a new substance that has entirely different chemical and physical properties. For example, when you bake a cake, you use butter, flour, sugar, and eggs. These ingredients each have different chemical and physical properties. However, they undergo chemical changes that turn them into a cake when they are baked together. Similarly, when a car rusts in the presence of moisture, iron and oxygen combine and form iron(III) oxide. In a chemical reaction, the substances present at the start of the reaction are called reactants, and the substances that are newly formed are called products. In the case of the rusting car, the reactants are iron and oxygen and the product is iron(III) oxide—the rust. Another common example of a chemical reaction is the combination of hydrogen gas and oxygen gas to form water. In this case, hydrogen and oxygen are the reactants and water is the product.

Decomposition Reactions

A decomposition reaction is the reverse of a combination reaction. Recall that in a decomposition reaction, one reactant breaks down into two or more products. The general form for a decomposition reaction is XY → X + Y. In such a reaction, the reactant is always a single compound, which is usually stable, so a source of energy must be provided to enable such reactions. You can predict the products of such reactions to be elements or compounds formed by splitting the reactant compound. For example, when magnesium phosphide is heated, it undergoes a decomposition reaction. Note that in this reaction, energy is provided in the form of heat. The predicted products of this reaction are magnesium and phosphorus. Notice how heat is shown on top of the equation arrow to indicate that heat is required for the reaction to occur. A decomposition reaction may also occur when energy is provided in the form of light or electricity. For example, when silver bromide is exposed to light, it undergoes a decomposition reaction. You can predict that the products of this reaction are silver metal and bromine gas because the reactant, silver bromide (AgBr) is made up of silver (Ag) and bromine (Br). The process of decomposing silver bromide is widely used in black-and-white photography to develop photography films. Chemically, this reaction can be shown as:

Word Equations

A thorough knowledge of chemical equations is required to understand how chemical reactions take place. Chemical equations are a shorthand way of describing the composition and amounts of all reactants and products in the reaction. Consider your face a product made up of reactants (or organs) such as a pair of eyes, ears, lips, and a nose. So, if you were able to describe your face using a word equation, it would look something like this: eye + nose + ears + lips → face (reactants) (product) A word equation is an accurate statement but it has a few drawbacks. First, it's not a universal statement. A French chemist would not necessarily understand the meaning of these English terms. Second, a word equation is a qualitative statement, not a quantitative one. It tells us in broad terms which reactants are involved, but it does not tell us how much of each substance. To overcome the first drawback, scientists created symbols for each of the elements, such as H for hydrogen and O for oxygen. They also developed a system of nomenclature that allows each substance to be represented by a formula. So, the word water might not make sense to a French scientist, but the molecular formula, H2O, would be instantly recognizable. To overcome the second drawback, scientists figured out a way to balance equations so that the equation represents the precise number of reactants involved

Balancing Chemical Equations

Balancing an equation is important because it gives you information about the exact number of reactants required to make the product. For example, with the "face equation" we know that a face is formed only when two eyes, two ears, two lips, and one nose are available. You can't make a proportioned face with one eye or two noses. To get the desired product, you need to mix the reactants in a certain ratio. A balanced chemical equation takes care of that ratio. Before you learn how to balance chemical equations, remember that a properly balanced chemical equation should follow the law of conservation of mass. Therefore, each side of the equation must contain the same number of atoms of each element. Now, let's start the balancing act! The first step in balancing a chemical equation is to ensure that the chemical formulas of the reactants and products are correct. Let's consider the formation of water molecules. Using the correct formulas for molecular hydrogen, molecular oxygen, and water, we can form the following skeleton equation: H2 + O2 → H2O A quick look at this equation will show you that it is not balanced. This is because while there are two atoms of hydrogen on both sides of the equation, there are two atoms of oxygen on the left side and only one atom on the right. This means that one atom of oxygen is unaccounted for. Since matter is always conserved, this is an unacceptable situation. One tempting way to balance the equation H2 + O2 → H2O is to remove the subscript from the oxygen molecule. But changing a subscript in a chemical formula changes the actual identity of the substance. For example, removing one oxygen atom from a carbon dioxide molecule turns it into the highly toxic carbon monoxide molecule. Similarly, molecular oxygen consists of two atoms of oxygen, not one. Instead of changing the subscript, how about multiplying the amount of products or reactants? This is acceptable since it only changes the amounts of the substances, not their identities. In the equation above, we need two atoms of oxygen on the right to balance the two atoms of oxygen on the left. We can do that by doubling the number of water molecules, as shown in the equation below. So the coefficient 2 is placed in front of H2O, making it 2H2O. A whole number coefficient in front of a chemical formula tells how many units of that substance are needed for the reaction. H2 + O2 → 2H2O Now, we have two molecules of water on the right, totalling two atoms of oxygen and four atom of hydrogen. But on the left, there's only two atoms of each. The oxygen atoms are balanced, but not the hydrogen atoms. Let's handle them next. We can summarize the process of balancing an equation into the following steps: Write an unbalanced equation using the correct chemical formulas. Balance each element one at a time by inserting appropriate coefficients. If a coefficient is absent, it is assumed to be 1. Do not change the subscripts of the formula. Check whether the number of atoms of each element is equal on both sides of the equation. Reduce all the coefficients of the equation to their lowest possible ratio. You can use the Equation Balancer tool to balance a chemical equation. In the tool, analyze the equation and enter the appropriate coefficients in the boxes provided to balance the equation. If the reactant or product does not require a coefficient, enter a 1 in the box. Now balance the following chemical equation yourself. Click the link below to load the equation in the Equation Balancer tool. Cu + S → Cu2S (Note: This equation is unbalanced as written.)

Reversible Reactions

Chemical reactions do not always convert reactants completely into products. Many chemical reactions are reversible, which means that the reactants react to form products and the products simultaneously break up to form the reactants. In other words, reversible reactions proceed in both the forward and reverse directions simultaneously. One example of a reversible reaction is the reaction of nitrogen gas and hydrogen gas to form ammonia gas. The chemical equation is shown above. The forward reaction is read from left to right, where nitrogen gas reacts with hydrogen gas to form ammonia. The reverse reaction is read from right to left to show that ammonia breaks up into hydrogen gas and nitrogen gas. Instead of writing two equations, a double arrow is used to indicate that both reactions are happening at the same time. A reversible reaction contains two reactions that occur simultaneously in opposite directions and therefore has the potential to achieve chemical equilibrium.

Products of Combustion Reactions

Do you recall that combustion reactions occur when oxygen reacts with other elements or compounds resulting in the production of heat and light? This type of reaction usually occurs when you burn any form of fossil fuel in the presence of oxygen. The general form for a combustion reaction is CxHy + O2 → CO2 and H2O (complete combustion). From the general formula, you can see that this type of reaction requires the reactants to include a compound-containing carbon, hydrogen, and in some cases, oxygen. A good way to predict such reactions is that the reactants usually include a hydrocarbon and the products include carbon dioxide and water. For example, when oxygen is abundant, acetylene burns completely to produce carbon dioxide and water. The equation can be written as C2H2(l) + O2(g) → CO2(g) + H2O(g). In some cases, the hydrocarbons don't burn completely and the combustion is incomplete due to insufficient quantities of oxygen. In such cases, carbon monoxide or carbon is produced. For example, if methane has insufficient oxygen during combustion, it produces carbon and water. One possible equation for incomplete combustion of methane is CH4(g) + O2(g) → C(s) + 2H2O(g). A reaction similar to combustion takes place in our bodies during digestion. However, in this case, carbohydrates, instead of hydrocarbons, react with oxygen to produce oxygen and water. This reaction can be shown as C6H12O6 + O2(g) → CO2(g) + H2O(l).

Chemical Equations

Let's go back to our word equation and apply what we just learned. Now, instead of using words in our "face equation" that may only be understood by those who speak the language, we can use symbols. For example, Ey will represent an eye, N for nose, Er for an ear, and L for a lip. These symbols can be universally understood by everyone. Using these symbols, this is how the equation would look: Ey + N + Er + L → EyNErL (reactants) (product) But we know that a face has to have two eyes, two ears, two lips, and one nose. So, the equation of a face that represents the correct number of reactants and product would be expressed as: 2Ey + N + 2Er + 2L → Ey2NEr2L2 (reactants) (product) The above equation is now balanced. This means that the number of ingredients in the reactants is equal to the number of ingredients in the product. In other words, it follows the law of conservation of mass. Let's learn more about this law.

Double-Replacement Reactions

Now let's move onto double-replacement reactions (also known as double-displacement reactions). These reactions occur between two ionic compounds when a cation from one compound replaces a cation from another compound. Generally, double-replacement reactions are represented by the following equation: AX + BY → BX + AY. In double-replacement reactions, the products may be a precipitate, water, or a gas. Let's look at a few examples of double-replacement reactions and find out how to predict the products of such reactions. When you combine a solution of potassium chloride with a solution of silver nitrate, a double-replacement reaction occurs. Since cations switch places during such reactions, we can predict that silver ions switch places with potassium ions to form silver chloride and potassium nitrate. This reaction can be shown as: AgNO3(aq) + KCl(aq) → AgCl(aq) + KNO3(aq). Since silver chloride is insoluble and potassium nitrate is soluble, silver chloride forms as a precipitate and potassium nitrate remains in solution. Generally, acids and bases undergo double-displacement reactions to produce water and salts. This special class of double-displacement reaction is called a neutralization reaction. As an example, the reaction between hydrochloric acid and sodium hydroxide forms sodium chloride and water: HCl(l) + NaOH(aq) → NaCl(aq) + H2O(aq). An example of a double-replacement reaction that produces gas may be seen when a solution of sodium sulfide is mixed with a solution of hydrochloric acid. We predict that the sodium and hydrogen cations will switch places to form hydrogen sulfide gas and sodium chloride; this can be written as Na2S(s) + HCl(l) → H2S(g) + NaCl(aq).

Combination and Decomposition Reactions

Recall that when hydrogen and oxygen combine, they form water and release energy. In 1937, this reaction took place with frightening force when the Hindenburg blimp, filled with hydrogen gas, exploded over New Jersey. The hydrogen gas in the blimp reacted with atmospheric oxygen to form water and a great deal of energy. Because of this tragedy, modern blimps now are filled with the nonreactive gas, helium. Such a reaction of hydrogen with oxygen is an example of a combination, or synthesis reaction. In this reaction, two or more reactants combine to produce one product. The general form of a combination reaction is as follows: X + Y → XY The reactants in a combination reaction can be either elements or compounds. But because the product of a combination reaction is always more complex than the reactants, it is always a compound.Let's take a look at a few common combination reactions: When a Group A metal cation reacts with a nonmetal, the product is an ionic compound. An example is this reaction of sodium and chlorine gas to produce sodium chloride or common table salt: 2Na + Cl2 → 2NaCl Compounds of nonmetals and oxygen, called nonmetal oxides, often combine with water to produce acids, which have low pH values. For example, carbon dioxide combines with water to produce carbonic acid. This reaction occurs in carbonated beverages such as soda pop where the carbonic acid formed is responsible for the fizz in sodas: H2O + CO2 → H2CO3 Metallic oxides combine with water to form bases, which have high pH values. For example, calcium oxide combines with water to yield calcium hydroxide: CaO + H2O → Ca(OH)2 Combination reactions also occur when metals combine with oxygen to form metal oxides. Play the video. It shows the combination reaction between sodium and oxygen, which forms the compound sodium oxide: Na + O2 → Na2O (Note: this equation is unbalanced as written.) Balance this equation now. Then return to the lesson and click Next to continue.ust as water molecules can be formed by the combination reaction of hydrogen and oxygen, they can be broken apart into oxygen and hydrogen atoms by using direct current electricity. This reaction can be chemically written as follows: 2H2O → 2H2 + O2 This reaction is the reverse of the combination reaction and is called a decomposition reaction. In a decomposition reaction, one reactant breaks down into two or more products. The general form for a decomposition reaction is this: XY → X + Y However, because the reactants are usually stable, energy in the form of heat, light, or electricity is often required for decomposition reactions to occur. Let's look at a few examples of decomposition reactions and the sources that trigger them.Light triggers a decomposition reaction when silver chloride—a light-sensitive crystalline solid—is exposed to light. Silver chloride decomposes in the presence of light to form silver metal and chlorine. Photography uses this decomposition reaction. Metallic silver produced in the reaction is deposited on the photography film to form an invisible, or latent, image. This image is developed later to form a visible image. 2AgCl → 2Ag + Cl2 Certain salts such as tin chloride can undergo electrolytic decomposition; that is, they break down into the elements, tin and chlorine, when exposed to direct current electricity: SnCl2 → Sn + Cl2 Some decomposition reactions occur spontaneously. In other words, they do not need energy. Carbonic acid, for example, decomposes spontaneously to give carbon dioxide and water. This reaction can be shown this way: H2CO3 → H2O + CO2

Combination Reactions

Recall that when two or more reactants combine to produce a product, it is called a combination reaction. Such a reaction generally involves two reactants—usually a metal and a nonmetal—that combine to form a single product. The general form of a combination reaction is: X + Y → XY The product of such a reaction is always a compound and is usually formed by the combination of metal and nonmetal reactants. It is also easy to predict a combination reaction because the product is always a combination of the reactants. For example, when barium combines with fluorine gas, it produces barium fluoride. Since barium forms a 2+ ion and fluorine forms a 1- ion, this reaction can be shown as Ba + F2 → BaF2. Notice how the product barium fluoride is written by simply combining both barium and fluorine. Similarly, when lithium reacts with oxygen, we can predict that the product will be a combination of both elements. Because lithium forms a 1+ ion and oxygen forms a 2- ion, the product is lithium oxide, or Li2O. Li + O2 → Li2O Notice that this equation isn't balanced because the numbers of lithium and oxygen atoms in the reactants are not equal to their numbers in the product.

Products of Single-and Double-Replacement Reactions

Single-Replacement Reactions Recall that during a single-replacement reaction, the lone element reactant replaces another element in the compound reactant to produce a new compound and a lone element. The lone element can be either a metal or a nonmetal. Single-replacement reactions have the following general form: AX + B → BX + A Notice how the lone element B replaces element A in the compound. However, for the element B to be able to replace element A, it has to be more reactive than element A. You can refer to the activity series to identify which elements will replace other elements. For example, if you place a piece of aluminum metal in a solution of magnesium chloride, no reaction occurs because aluminum is less reactive than magnesium. However, if you dip a piece of magnesium in an aluminum chloride solution, a single-replacement reaction occurs in which magnesium replaces aluminum to form magnesium chloride and aluminum metal. Remember that in a single-replacement reaction, only a metal can replace another metal and a nonmetal can only replace another nonmetal. Let's take a look at the single-replacement reaction that occurs when copper reacts with silver nitrate. In this reaction, copper is the lone element and silver nitrate is a compound of silver and nitrate ion. Both copper and silver are metals, but copper is more reactive than silver. We can predict that during the reaction, copper will replace silver to form copper nitrate and silver will remain in the solution. This equation can be shown as: 2AgNO3(aq) + Cu(s) → Cu(NO3)2(aq) + 2Ag(s) The same holds true when non-metals react in a single replacement reaction, like when chlorine reacts with sodium bromide. Since chlorine is more reactive than bromine, chlorine replaces bromine to produce sodium chloride and aqueous bromine. The equation for this reaction is: NaBr(s) + Cl2(g) → Br2(aq) + NaCl(aq)

Combustion of Hydrocarbons

The fifth category of chemical reactions is the combustion reaction. When an organic substance combines with oxygen to produce heat and light, a combustion of a hydrocarbon reaction occurs. Many important combustion reactions occur with organic molecules called hydrocarbons, which are made up of only carbon and hydrogen, and produce carbon dioxide and water as products. Much of the energy used in your everyday life comes from combustion reaction of molecules with oxygen. For example, propane (C3H8) in a camp stove combines with oxygen to generate heat for cooking. This reaction can be written as follows: C3H8 + 5O2 → 3CO2 + 4H2O Gasoline (C8H18) reacts with oxygen, and when burned, it generates enough energy to power a car. This reaction can be written as follows: C8H18 + O2 → CO2 + H2O (Note that this equation is unbalanced as written.)The previous examples showed how carbon dioxide is produced when you burn a substance in the presence of oxygen. However, carbon dioxide isn't always the product. If hydrocarbons burn in insufficient amounts of oxygen, carbon monoxide (CO) forms instead of carbon dioxide. Formation of carbon monoxide results from incomplete combustion of carbon when there is not enough oxygen. While carbon dioxide is relatively nontoxic and is generated by animals and used by plants, carbon monoxide is a poisonous gas even at very low concentrations. For this reason, combustion reactions should always take place in well-ventilated areas. For example, wood combusts with oxygen, just as a hydrocarbon does. If you burn wood in a fireplace with a closed flue, the room may fill with toxic carbon monoxide due to incomplete combustion. Incomplete combustion can also produce soot, which consists of carbon particles. A typical campfire will produce carbon dioxide, carbon monoxide, and soot, depending on the availability of oxygen in a given part of the campfire. Combustion reactions also occur in the human body during metabolism. The energy produced during these reactions is necessary for the functioning, growth, and reproduction of most living organisms. Carbohydrates are molecules associated with living organisms. In contrast to hydrocarbons, carbohydrates contain carbon, hydrogen, and also oxygen. Glucose and other sugars are carbohydrates as are many other complex molecules. Carbohydrates react with plentiful oxygen in organisms to produce carbon dioxide and water. This reaction occurs much more slowly than the burning of hydrocarbons, though. The reaction of carbohydrates with oxygen in organisms is called metabolism instead of combustion, but the products are the same. The equation for the combustion of glucose is as follows: C6H12O6 + 6O2 → 6CO2 + 6H2O Fats and proteins are also metabolized in organisms to produce carbon dioxide and water, but proteins also produce nitrogen compounds. Metabolism of substances in your body with insufficient oxygen results in the lower energy production along with potentially toxic products, such as ethanol and lactic acid.

Double-Replacement and Acid-Base Reactions

The fourth category of chemical reactions is the double-replacement reaction. This reaction is also called double-displacement reaction and has this general form: AX + BY → BX + AY This type of reaction involves the exchange of cations between two compounds. For example, if you mix solutions of lead nitrate and potassium chloride, lead cations bond to chloride anions and settle on the bottom as a white solid. Potassium cations and nitrate anions combine to form potassium nitrate, which exists in aqueous state (by its nature, it is a soluble ionic substance). The white solid that settles to the bottom is lead chloride and is referred to as a precipitate (by its nature, it's an insoluble ionic substance). This reaction is a double-displacement reaction because an exchange of atoms or ions occurs between compounds and is written as follows: Pb(NO3)2(aq) + 2KCl(aq) → PbCl2(s) + 2KNO3(aq) Double-displacement reactions can be of three types depending on the nature of the products: a product could be a solid that precipitates out of the solution, a product could be a gas, or it could be water. Let's look at some examples of double-replacement reactions and the products. The reaction between aqueous solutions of sodium sulfide and cadmium nitrate is an example of a double-replacement reaction forming a precipitate. A yellow precipitate of cadmium sulfide is formed. This is the equation for this reaction: Na2S(aq) + Cd(NO3)2(aq) → CdS(s) + 2NaNO3(aq) Gas is formed as a product in a double-replacement reaction between hydrochloric acid and sodium sulfide. Hydrogen sulfide gas is produced and bubbles out of the solution, while sodium chloride remains in the solution. This is the equation for this reaction: 2HCl(aq) + Na2S(aq) → H2S(g) + 2NaCl(aq) Water is formed as a product in the double-replacement reaction between sulfuric acid and aluminum hydroxide. In this reaction, aluminum sulfate salt is also generated: 3H2SO4(aq) + 2Al(OH)3(aq) → Al2(SO4)3(aq) + 6H2O(l) This double-replacement reaction is an example of an acid-base neutralization reaction. In short, double-displacement reactions involving an acid and a base resulting in the formation of salt and water are acid-base neutralization reactions: acid + base → salt + water

Law of Conservation of Mass

The law of conservation of mass states that matter can neither be created nor destroyed. So, the products formed in a reaction must have the same total mass as that of the reactants present before the reaction took place. On the other hand, atomic theory—the study of matter—says that atoms maintain their identities in a chemical reaction. These statements taken together mean that any equation for a reaction must be balanced. There must be as many atoms of each element on the products side as there are on the reactants side. You will learn how to balance equations later in this lesson. First, let's explore the components of an equation.

Oxidation-Reduction Reactions

The sixth category of chemical reactions is the oxidation-reduction reaction, better known as the redox reaction. Rusting is a very common redox reaction. If an iron nail is exposed to air for a long time, it combines with oxygen in the air, in the presence of moisture, to form iron(III) oxide, rust. The rusting of iron can be written as follows: 4Fe + 3O2 → 2Fe2O3 This reaction is an oxidation reaction where iron reacts with oxygen to form an oxide. Although rusting is a reaction of iron with oxygen, it is not a combustion of a hydrocarbon reaction since it does not involve burning, and water and carbon dioxide are not formed as products. In fact, combustion is a type of oxidation reaction because it too produces oxide of carbon, CO2. Conversely, when a compound loses oxygen, a reduction reaction takes place. For example, iron(III) oxide can be reduced to metallic iron by heating it in the presence of carbon: 2Fe2O3 + 3C → 4Fe + 3CO2 Note that as iron oxide is reduced, carbon is oxidized to carbon dioxide. In oxidation-reduction reactions, when one compound is oxidized, the other is reduced. But, oxidation and reduction do not always involve oxygen. Let's see how such reactions are described.

Single-Replacement Reactions

The third category into which chemical reactions fall is the single-replacement reaction; this reaction is also known as a single-displacement reaction. In a single-replacement reaction, one element takes the place of another element in a compound. A single-replacement reaction has this general form: AX + B → BX + A A so-called violent single-replacement reaction occurs when a piece of metallic potassium is placed in a dish of water. Potassium displaces one of the hydrogen atoms in a water molecule producing hydrogen gas and aqueous potassium hydroxide, as shown in the equation. In this case, potassium takes the place of one of the hydrogen atoms in a water molecule. 2K(s) + 2H20(l) → 2KOH(aq) + H2(g) A less dramatic single-replacement reaction takes place when a strip of zinc metal is placed in a solution of copper sulfate. The zinc replaces the copper ion in the solution and forms zinc sulfate, as shown in the equation. The copper that is displaced is deposited on the zinc strip. CuSO4(aq) + Zn(s) → ZnSO4(aq) + Cu(s) It's important to note that not all elements can displace other elements in single-displacement reactions. For example, on the previous screen, zinc displaced copper from a solution of copper sulfate. However, the reverse is not possible: copper cannot spontaneously displace zinc from a solution containing zinc ions. In fact, chemists have experimentally determined which metals displace other metals. The results can be displayed on a chart, showing the hierarchy of displacements. Any element in the chart displaces the elements below it and is displaced by the elements above it. This arrangement of metal elements is known as the activity series and shows the relative reactivity of each metal element. Thus, you can see that lithium will displace any metal on the chart, and any metal will displace gold. You may have noticed that the element hydrogen is on the activity chart with the metals even though hydrogen is not a metal. It is placed there because in replacement reactions, hydrogen behaves like a metal; that is, it donates electrons during bond formation The activity series can be used to predict the outcomes of reactions. For example, in the single-replacement reaction demonstrated earlier, the displacement of copper and the formation of zinc sulfate could have been predicted because zinc is higher on the chart than copper and thus is more reactive. So, if you were to place a copper wire into a solution of silver nitrate, would the copper displace the silver? Looking at the activity series, you can see that it would. Silver metal will be deposited and aqueous copper(II) nitrate would form, giving the solution a bluish tint. Below is the equation for this reaction: 2AgNO3(aq) + Cu(s) → Cu(NO3)2(aq) + 2Ag(s) Now can you guess what would happen if you placed silver into copper(II) nitrate solution? In this case, a look at the activity series tells you that no reaction will take place because silver is less reactive than copper.Take a look at the activity series of common metals. Observe how the reactivity with water changes. Highly reactive metals such as lithium and potassium react with cold water. Less reactive metals such as magnesium and aluminum react with steam whereas metals less reactive than these react only with acids. You may want to save or print the activity series document for future reference. Single-replacement reactions also occur when nonmetal elements displace other nonmetal elements. In halogens, reactivity follows specific trends down the group in the periodic table. Recall the trends of other properties such as electronegativity and ionization energy in the periodic table. Halogens have decreasing reactivity going down the group with fluorine being the most reactive and iodine being the least reactive. A halogen can displace any halogen ion that appears below it: bromine can displace iodine, but it cannot displace chlorine. Here are the reactions: Br2(l) + 2NaI(aq) → 2NaBr(aq) + I2(s) Br2(l) + 2NaCl(aq) → no reaction Other nonmetals also show trends in displacement. With the exception of the nonreactive noble gases, nonmetals on the right of the periodic table or higher on the chart tend to displace those that are lower in the chart or are located on the left of the periodic table. Knowing this, you can predict that sulfur will not displace oxygen from zinc oxide because sulfur is lower on the periodic table than oxygen.

The four steps to balance a chemical equation are

Write an unbalanced skeleton equation using the correct chemical formulas. Balance each element in the equation one at a time by inserting appropriate coefficients. If a coefficient is absent, it is assumed to be 1. Do not change the subscripts of the formula. Check whether the number of atoms of each element is equal on both sides of the equation. Reduce all the coefficients of the equation to their lowest possible ratio.