Video Transcript
The decomposition of calcium
nitrate proceeds according to the following equation: two Ca(NO3)2 solid plus 369
kilojoules reacts to produce two CaO solid plus four NO2 gas plus O2 gas. How much energy is needed to
decompose 3.2 moles of calcium nitrate? Give your answer as a whole
number.
During a chemical reaction, energy
may be gained and/or lost by the system in the form of heat, light, and/or
sound. The net change in the internal
energy of a system is called the change in enthalpy. The change in enthalpy is the net
amount of energy absorbed or released by a chemical reaction. The change in enthalpy can be
included in the chemical equation. In the given chemical equation, the
change in enthalpy is written as a reactant. This means that the reaction is an
endothermic process, a process that absorbs energy from the surroundings.
To answer the question, we need to
determine how much energy is needed to decompose a certain amount of calcium
nitrate. Looking at the reaction equation,
we can see that this equation describes the decomposition of two moles of calcium
nitrate. But we want to know how much energy
is needed to decompose 3.2 moles of calcium nitrate. The amount of energy required for
the reaction is proportional to the number of moles. So we could use a proportion to
answer this question. We know that 369 kilojoules of
energy is required to decompose two moles of calcium nitrate. We want to know how much energy,
represented by 𝑥, is needed to decompose 3.2 moles of calcium nitrate.
Notice that when setting up the
proportion, we made sure that the units in the numerator and the units in the
denominator matched on both sides of the proportion equation. To solve for 𝑥, we need to
multiply both sides of the equation by 3.2 moles. This will cancel the 3.2 moles on
the right-hand side of the equation.
Now, we simply need to perform the
calculation to solve for 𝑥. The mole units will cancel, leaving
us with the unit kilojoules. After performing the calculation,
we have determined that 𝑥 is equal to 590.4 kilojoules. The question asks us to give our
answer as a whole number. Rounding appropriately, we have
determined that the amount of energy needed to decompose 3.2 moles of calcium
nitrate is 590 kilojoules.
