Question Video: Calculating the Amount of Energy Needed to Decompose a Given Amount of Calcium Nitrate | Nagwa Question Video: Calculating the Amount of Energy Needed to Decompose a Given Amount of Calcium Nitrate | Nagwa

# Question Video: Calculating the Amount of Energy Needed to Decompose a Given Amount of Calcium Nitrate Chemistry • First Year of Secondary School

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The decomposition of calcium nitrate proceeds according to the following equation: 2 Ca(NO₃)₂ (s) + 369 kJ ⟶ 2 CaO (s) + 4 NO₂ (g) + O₂ (g). How much energy is needed to decompose 3.2 moles of calcium nitrate? Give your answer as a whole number.

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### 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.

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