Chemical Reactions - AP Chemistry

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Question

For single replacement reactions, which of the following sets of guidelines are most helpful?

Answer

When writing/balancing a single replacement reaction, make sure to consult the activity series, because that will tell us if a reaction will actually take place. Remember to look at the cations (metals and hydrogen) and where they are in relation to each other on the activity series. The higher one on the activity series is the most reactive; so if the cation by itself is the most reactive, it will replace the other cation and a reaction will occur. Boyle's law explains the inverse relationship between volume and pressure with respect to certain amount of an ideal gas at constant temperature.

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Question

What is the chemical formula of the salt formed when a chemist mixes solvated Potassium and Arsenic ions in solution?

Answer

Potassium is a Group I element, so to get to a filled valence shell, it will lost one electron, yielding $K^+$ .

Arsenic is a Group 5 element, so it needs to gain three electrons to obtain a filled valence shell, yielding $As^{-3}$ .

In order to balance out the charges, the resultant salt will be $K_3As$ .

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Question

What is the net ionic equation for the ion exchange reaction between ferrous sulfate and calcium iodide? Assume all compounds are soluble.

Answer

First, we must know what ferrous sulfate is. Ferrous refers to $Fe^{2+}$ , and sulfate has the formula $SO_4^{-2}$ . When we combine the two together we get .

Calcium is a divatent cation and iodide is a monovalent anion, so their salt is . The ion exchange reaction is then:

$FeSO_4 + CaI_2 \rightarrow FeI_2 +CaSO_4$

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Question

Select the net ionic equation from this molecular reaction:

$Ba(NO_{3})_{2} (aq) + K_{2}SO_{4} (aq) \rightarrow 2KNO_{3} (aq) + BaSO_{4} (s)$

Answer

The net ionic equation is derived by removing all spectator ions from the total ionic equation (in which all ions are listed). To put it another way, the net ionic equation involves only the ions that participate in a reaction which, in this case, is the precipitation of barium sulfate.

Begin by writing all aqueous compounds in their dissociated (ionic) forms.

$Ba(NO_{3})_{2} (aq) + K_{2}SO_{4} (aq) \rightarrow 2KNO_{3} (aq) + BaSO_{4} (s)$

$Ba^{2+}+2NO_3^-+2K^++SO_4^{2-}\rightarrow2K^++2NO_3^-+BaSO_4(s)$

Cancel out any ions that appear in equal quantities on both sides of the equation. In this case, we can cancel the nitrate and potassium ions.

$Ba^{2+}+SO_4^{2-}\rightarrow BaSO_4(s)$

This is our net ionic equation.

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Question

$CaCO_{3} (s) \rightarrow CaO (s) + CO_{2} (g)$

The reaction above could be classified as __________.

Answer

When one molecule is converted into two or more smaller molecules, the reaction is considered a decomposition reaction. In this example, none of the elements under go a change in oxidation number, so this is not an oxidation-reduction reaction. (Calcium is always , oxygen is always , and carbon remains throughout the reaction.)

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Question

What is the balanced chemical equation for the combustion of butane $(C_4H_{10})$ ?

Answer

Combustion is the chemical reaction of a hydrocarbon with molecular oxygen, and it always produces carbon dioxide and water. Knowing the reactants and products, the unbalanced equation must be:

$C_4H_{10} + O_2 \rightarrow CO_2 + H_2O$

We start by balancing the hydrogens. Since there are 10 on the left and only 2 on the right, we put a coefficient of 5 on water.

$C_4H_{10} + O_2 \rightarrow CO_2 + 5H_2O$

Similarly, we balance carbons by putting a 4 on the carbon dioxide.

$C_4H_{10} + O_2 \rightarrow 4CO_2 + 5H_2O$

To find the number of oxygens on the right, we multiply the 4 coefficient by the 2 subscript on O (which gets us 8 oxygens) and then add the 5 oxygens from the 5 water molecules to get a total of 13. The needed coefficient for on the left would then have to be 13/2.

$C_4H_{10} + \frac{13}{2}O_2 \rightarrow 4CO_2 + 5H_2O$

Because fractional coefficients are not allowed, we mutiply every coefficient by 2 to find our final reaction:

$2C_4H_{10} + 2\frac{13}{2}O_2 \rightarrow 24CO_2 + 2*5H_2O$

$2C_4H_{10} + 13O_2 \rightarrow 8CO_2 + 10H_2O$

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Question

Determine whether or not solid aluminum reacts with aqueous zinc chloride. If it does, determine the balanced equation for the reaction.

Answer

When we check the activity series, it is fairly easy to see that aluminum metal is more reactive than zinc metal. So, in this case, the two metals undergo a redox reaction, where the aqueous $Zn^{2+}$ is reduced to solid , and the solid is oxidized to aqueous $Al^{3+}$ . These charges are the common oxidation states for zinc and aluminum and should be memorized.

Because $Al^{3+}$ is the new species, it bonds with 3 ions. The unbalanced equation is:

$Al(s) + ZnCl_2(aq) \rightarrow AlCl_3 (aq) + Zn (s)$

We note that there are 2 chlorine atoms on the left and 3 chlorine atoms on the right. To balance, we use a 3 coefficient on the left and a 2 coefficient on the right. This gives a total of 6 chlorine atoms on eahc side.

$Al(s) + {\color{Red} 3}ZnCl_{\color{Blue} 2}(aq) \rightarrow{\color{Blue} 2}AlCl_{\color{Red} 3} (aq) + Zn (s)$

However, now we have also increased the amounts of zinc and aluminum. We copy the necessary coefficients to balance those—2 for aluminum on the left, 3 for zinc on the right—and we are done:

$2Al(s) + 3ZnCl_2(aq) \rightarrow 2AlCl_3 (aq) + 3Zn (s)$

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Question

$Ba(NO_3)_2_{(aq)}+Na_2SO_4_{(aq)}\rightarrow BaSO_4_{(s)}+2NaNO_3_{(aq)}$

What is the net ionic form of this equation?

Answer

To find the net ionic form of this chemical equation, first balance the equation, then dissociate all soluble components. In other words, separate the aqueous terms into two separate molecules/atoms. For example, $Ba(NO_3)_2_{(aq)}$ dissociates into $Ba^{2+}$ and $NO_3^{-}$ . After separating all soluble terms, balance the equation and cancel out any terms that repeat on both sides of the equation. For example, $NO_3^{-}$ will be on both sides of the equation after separating all terms so you can cross them out. Below are the steps taken to find the net ionic form of this chemical equation.

$Ba(NO_3)_2_{(aq)}+Na_2SO_4_{(aq)}\rightarrow BaSO_4_{(s)}+2NaNO_3_{(aq)}$

Write out the dissociated forms of each species, if applicable.

$Ba^{2+}+ 2NO_3^{-}+ 2Na^++SO_4^{2-}\rightarrow BaSO_4_{(s)}+2Na^++ 2NO_3^{-}$

Cross out species that appear on both sides of the equation. The net ionic equation is:

$Ba^{2+}+SO_4^{2-}\rightarrow BaSO_4_{(s)}$

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Question

$\small FeS + 2HCl \rightarrow FeCl_{2} + H_{2}S$

What type of reaction is shown above?

Answer

The typical double replacement reaction is as follows:

$\small AB + XY \rightarrow AY + XB$

$\small A= Fe, B = S, X =H, Y = Cl$

The anions are the chemical species being exchanged (both sulfur and chloride). Hence, the name double replacement is given to this particular reaction.

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Question

Which of the following represents a combustion reaction?

Answer

Combustion reactions always produce $\small CO_{2} + H_{2}O$ and excess heat. Depending on the molecule that is oxidized by oxygen, which in this case was methane $\small (CH_{4})$ , the ratios between $\small CO_{2}$ and $\small H_{2}O$ can vary.

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Question

Given that lithium is higher on the activity series than hydrogen, what should be seen when solid lithium and hydrochloric acid are mixed?

Answer

Given that lithium is more reactive than hydrogen, expect a single replacement reaction to take place, so lithium will replace hydrogen.

$Li_{(s)}+HCl\rightarrow LiCl(s) + H_{2}$

All ionic compounds are solids at room temperature, which is why lithium chloride has the solid phase label. Remember that hydrogen is a diatomic element which is a gas a room temperature. When observing reactions in which gasses are produced from a solution, bubbles are seen. There is no indication whether this reaction is endothermic or exothermic, nor is there any information that suggests the reaction should change color.

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Question

The following unbalanced reaction is important in the process of Steel Manufacturing:

$Fe_2O_3_{(s)} + C_{(g)} \rightarrow Fe_{(l)} + CO_{(g)}$

Balance the following equation and name it's reaction type:

$Fe_2O_3_{(s)} + C_{(g)} \rightarrow Fe_{(l)} + CO_{(g)}$

Answer

Use the following steps to balance the equation:

1.) Check for diatomic molecules: in this case there are none so move on to step 2

2.) Balance the metals (hydrogen is not considered a metal in this application): There are 2 iron atoms on the left hand side and 1 iron atom on the right hand side so we add a 2 in front of the Fe on the right hand side to give:

$Fe_2O_3_{(s)} + C_{(g)} \rightarrow 2Fe_{(l)} + CO_{(g)}$

3.) Balance the nonmetals (not including oxygen). There is one carbon on both sides so move on to step 4

4.) Balance oxygen. There are 3 oxygens on the left hand side and only 1 on the right hand side, so we can add a 3 in front of carbon monoxide on the right hand side to give:

$Fe_2O_3_{(s)} + C_{(g)} \rightarrow 2Fe_{(l)} + 3CO_{(g)}$

5.) Balance hydrogen. No hydrogens, so we move on.

6.) Recount all atoms to make sure you have balanced correctly. There are 2 iron atoms on both sides and 3 oxygen on both sides. However our carbons are no longer balanced so we can add a 3 in front of the elemental carbon on the left hand side to give:

$Fe_2O_3_{(s)} + 3C_{(g)} \rightarrow 2Fe_{(l)} + 3CO_{(g)}$

If this problem had involved ionic species you would also want to make certain that the charges are balanced on both sides of the equation.

The charges on both sides add up to zero so your equation is balanced:

$Fe_2O_3_{(s)} + 3C_{(g)} \rightarrow 2Fe_{(l)} + 3CO_{(g)}$

Single v.s Double Replacement Reaction:

Single replacement Reaction:

A single replacement reaction is defined as a type of reduction-oxidation reaction in which a more active element replaces a less active element in a compound. These reactions produce a new compound and an element as the products.

General chemical equation:

$X + YZ \rightarrow XZ + Y$

Double Replacement Reaction:

A double replacement reaction is a type of reaction in which two reacting chemical species exchange bonds (ionic or covalent) resulting in the creation of two new products.

General chemical equation:

$AB + CD \rightarrow AD + CB$

$2Fe_2O_3_{(s)} + 3C_{(g)} \rightarrow 4Fe_{(l)} + 3CO_2_{(g)}$ is also important in steel manufacturing and is a single replacement reaction. However, the equation given was $Fe_2O_3_{(s)} + C_{(g)} \rightarrow Fe_{(l)} + CO_{(g)}$ so the difference being carbon monoxide production rather than carbon dioxide production. In reality both reactions occur simultaneously.

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Question

What is used as guidelines to determine the phase labels for double displacement/double replacement reactions?

Answer

For double displacement, the solubility rules determine the phase labels. Make sure the correct set of rules/guidelines for the type of reaction that is being written/balanced are used. The octet rule refers to the stability atoms achieve by filling their outer shell of electrons. Huckel number is 4n+2 where n is any integer, and is involved in assigning aromaticity.

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Question

$MnO_{4}^{-} + e^{-} + H^{+} \rightarrow Mn^{2+} + H_{2}O$

What is the coefficient for $H^{+}$ , reduced to the lowest whole number, when the given reaction is balanced?

Answer

The best way to solve this problem is to try all the possible answers. When we try 8, $8H^{+}$ means that there must be $4H_{2}O$ . $4H_{2}O$ means that there must be just $1 MnO_{4}^{-}$ , which means that there is $1 Mn^{2+}$ . When $Mn^{7+}$ is reduced to $Mn^{2+}$ , there are 5 remaining electrons. So 8 is correct. Alternatively, this question may be answered by the classical "trial and error" method of balancing equations.

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Question

For single replacement reactions, which of the following sets of guidelines are most helpful?

Answer

When writing/balancing a single replacement reaction, make sure to consult the activity series, because that will tell us if a reaction will actually take place. Remember to look at the cations (metals and hydrogen) and where they are in relation to each other on the activity series. The higher one on the activity series is the most reactive; so if the cation by itself is the most reactive, it will replace the other cation and a reaction will occur. Boyle's law explains the inverse relationship between volume and pressure with respect to certain amount of an ideal gas at constant temperature.

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Question

What is the chemical formula of the salt formed when a chemist mixes solvated Potassium and Arsenic ions in solution?

Answer

Potassium is a Group I element, so to get to a filled valence shell, it will lost one electron, yielding $K^+$ .

Arsenic is a Group 5 element, so it needs to gain three electrons to obtain a filled valence shell, yielding $As^{-3}$ .

In order to balance out the charges, the resultant salt will be $K_3As$ .

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Question

What is the net ionic equation for the ion exchange reaction between ferrous sulfate and calcium iodide? Assume all compounds are soluble.

Answer

First, we must know what ferrous sulfate is. Ferrous refers to $Fe^{2+}$ , and sulfate has the formula $SO_4^{-2}$ . When we combine the two together we get .

Calcium is a divatent cation and iodide is a monovalent anion, so their salt is . The ion exchange reaction is then:

$FeSO_4 + CaI_2 \rightarrow FeI_2 +CaSO_4$

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Question

Select the net ionic equation from this molecular reaction:

$Ba(NO_{3})_{2} (aq) + K_{2}SO_{4} (aq) \rightarrow 2KNO_{3} (aq) + BaSO_{4} (s)$

Answer

The net ionic equation is derived by removing all spectator ions from the total ionic equation (in which all ions are listed). To put it another way, the net ionic equation involves only the ions that participate in a reaction which, in this case, is the precipitation of barium sulfate.

Begin by writing all aqueous compounds in their dissociated (ionic) forms.

$Ba(NO_{3})_{2} (aq) + K_{2}SO_{4} (aq) \rightarrow 2KNO_{3} (aq) + BaSO_{4} (s)$

$Ba^{2+}+2NO_3^-+2K^++SO_4^{2-}\rightarrow2K^++2NO_3^-+BaSO_4(s)$

Cancel out any ions that appear in equal quantities on both sides of the equation. In this case, we can cancel the nitrate and potassium ions.

$Ba^{2+}+SO_4^{2-}\rightarrow BaSO_4(s)$

This is our net ionic equation.

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Question

$CaCO_{3} (s) \rightarrow CaO (s) + CO_{2} (g)$

The reaction above could be classified as __________.

Answer

When one molecule is converted into two or more smaller molecules, the reaction is considered a decomposition reaction. In this example, none of the elements under go a change in oxidation number, so this is not an oxidation-reduction reaction. (Calcium is always , oxygen is always , and carbon remains throughout the reaction.)

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Question

What is the balanced chemical equation for the combustion of butane $(C_4H_{10})$ ?

Answer

Combustion is the chemical reaction of a hydrocarbon with molecular oxygen, and it always produces carbon dioxide and water. Knowing the reactants and products, the unbalanced equation must be:

$C_4H_{10} + O_2 \rightarrow CO_2 + H_2O$

We start by balancing the hydrogens. Since there are 10 on the left and only 2 on the right, we put a coefficient of 5 on water.

$C_4H_{10} + O_2 \rightarrow CO_2 + 5H_2O$

Similarly, we balance carbons by putting a 4 on the carbon dioxide.

$C_4H_{10} + O_2 \rightarrow 4CO_2 + 5H_2O$

To find the number of oxygens on the right, we multiply the 4 coefficient by the 2 subscript on O (which gets us 8 oxygens) and then add the 5 oxygens from the 5 water molecules to get a total of 13. The needed coefficient for on the left would then have to be 13/2.

$C_4H_{10} + \frac{13}{2}O_2 \rightarrow 4CO_2 + 5H_2O$

Because fractional coefficients are not allowed, we mutiply every coefficient by 2 to find our final reaction:

$2C_4H_{10} + 2\frac{13}{2}O_2 \rightarrow 24CO_2 + 2*5H_2O$

$2C_4H_{10} + 13O_2 \rightarrow 8CO_2 + 10H_2O$

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