3.1-3.7 Energetics

What is the definition of exothermic?

A reaction that releases heat energy, so temperature increases

What is the definition of endothermic?

A reaction that absorbs heat energy, so temperature decreases

What are the axis for an energy level diagram?

Y-axis, labelled chemical potential energy

No x-axis

If it is an exothermic reaction, how should the products be placed in an energy level diagram?

The products should be lower than the reactants

If it is an endothermic reaction, how should the products be placed in an energy level diagram?

The products should be higher than the reactants

How is enthalpy change indicated in an energy level diagram?

Enthalpy change indicated by a single-headed arrow pointing from reactants to products labelled ∆H

If it is an exothermic reaction, what is the sign of the enthalpy change?

Negative enthalpy change (-)

What are the units of enthalpy change?

kJ/mol

What is m in the formula Q = mc∆T?

Mass of the water/solution NOT including any solids added

What are two factors that lead to an error in combustion calorimetry?

1. Heat loss to the surroundings

2. Incomplete combustion of the fuel

Why does incomplete combustion of the fuel result in an inaccurate value of the enthalpy change?

Incomplete combustion releases less heat energy than complete combustion. Therefore, the experimentally calculated value of the enthalpy change is less exothermic than expected

Fill in the gaps:

1. Breaking bonds _ energy

2. Forming bonds _ energy

1. Breaking bonds requires energy

2. Forming bonds releases energy

Explain why the combustion of methane is an exothermic reactions in terms of bond-breaking and bond-forming:

The reaction is exothermic because more energy is released forming new bonds in the products than was required breaking the bonds in the reactants