General Topics - College Chemistry

A balanced chemical equation will have the same number of each atom on both sides of the reaction.

Start by balancing the number of nitrate.

Since we have nitrate on the left, we must also have nitrate on the right.

This equation now gives potassium on the left, and potassium on the right. Balance the potassium.

This equation is balanced because there are equal numbers of each atom on both sides.

Phosphoric acid combines a single phosphate ion with three hydrogen ions. The correct molecular formula is . is the molecular formula for hydrophosphoric acid, is the molecular formula for phosphorous acid, and is just a charged phosphate ion, which has biochemical significance with regards to DNA structure and energy molecules like ATP. Phosphorus is not a diatomic atom.

Start by finding the molar mass of of by adding up the molar masses of its constituent atoms.

Now, divide the molar mass of the molecule by the molar mass of its empirical formula.

In order to find the molecular formula, you will need to multiply the empirical formula by . Thus, the molecular formula is .

We're given the percent composition of the elements carbon and hydrogen in a given compound, and we're asked to determine the empirical formula.

The first thing we have to do is determine the relative molar ratios of each element. In this case, because we are given the percent composition, we can assume that we're starting off with of the starting material. That way, we can convert each percentage directly into grams.

Following that, we need to use the molar mass of each element in order to convert it from grams to moles.

In other words, what we have found is that in our compound, for every of carbon, there will also be of hydrogen.

But remember, the empirical formula for any given compound tells us the lowest whole number ratio of the compound's constituent elements. Therefore, we'll need to divide each value by the lowest number out of all the values available.

What this tells us is that for every of carbon in this compound, there will be of hydrogen as well. This is equivalent to the previous ratio, but now it has been reduced to the lowest possible whole numbers.

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:

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.

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

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.

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

A combustion reaction involves the release of heat from the burning of a hydrocarbon in oxygen to form carbon dioxide and water. The amount of hydrogen, carbon, and oxygen are conserved. This reaction is exothermic because of the high energy released when organic hydrocarbons are burned. It can be easily observed in the burning of petroleum distillates such as gasoline.

Recall that combustion equations are examples of reduction-oxidation reactions.

This cannot be a precipitation reaction because there are no solids in the products.

This cannot be a gas-evolution reaction because the reactants are not in aqueous form.

This cannot be an acid-base reaction because there is no proton transfer.

This is a basic identify the reaction type equation of the form:

Since both reactants are combined into one it is a combination reaction.

Now let's go over the wrong answers:

1. It isn't a single displacement because single displacement reactions are of the form:

1. It isn't a double displacement/metathesis reaction because double displacement reactions are of the form:

1. It isn't a decomposition reaction because decomposition reactions are the exact opposite of what occurs in the reaction in the problem. Meaning instead of two or more elements forming a compound, a compound breaks down into two or more elements.

1. It isn't a combustion reaction because a combustion reaction refers to the burning of a compound (usually a hydrocarbon) within which the other reactant is and the products are some amount of . So the general form of a combustion equation look as follows:

There are five main types of chemical reactions.

1. Synthesis reactions have the following format:

In these reactions, two substances combine to form one substance. This occurs when hydrogen and oxygen combine to form water:

1. Decomposition reactions have the following format:

In these reactions, a compound breaks down to form smaller substances. This occurs when some acids decompose into an acidic oxide and water:

1. Single displacement reactions have the following format:

In these reactions, a single element replaces another element in a compound. This occurs in the reaction between zinc and hydrochloric acid:

1. Double displacement reactions have the following format:

In these reactions, an element from each of the two reactant compounds switches places. This occurs in the reaction between sulfuric acid and sodium hydroxide:

1. Combustion reactions have the following format:

In these reactions, a hydrocarbon and oxygen always react to form carbon dioxide and water. Here is an example:

Start by balancing the given chemical equation:

Next, convert the grams of pentane into moles of pentane.

Use the stoichiometric ratio given by the balanced equation to find the number of moles of oxygen needed to react with the pentane.

Finally, convert the number of moles of oxygen into grams of oxygen.

There should be significant figures, so the answer is .

Start by balancing the equation:

Next, figure out which reactant is the limiting reactant.

Since fewer moles of is produced when is reacted, then must be the limiting reactant.

Convert the amount of moles of into grams.

Use the relations , molar mass , and

For this question, we're given the density and volume of a gas and we're asked to find the mass of the gas.

To answer this question, we'll need to use dimensional analysis. What this means is that we'll need to cancel out units in order to obtain the ones that we're looking for.