3 1 energetics

An exothermic reaction is a reaction that gives out heat energy to the surroundings causing the temperature of the surroundings to increase.

An endothermic reaction is a reaction that takes in heat energy from the surroundings causing the temperature of the surroundings to decrease.

True. Neutralisation reactions are exothermic reaction.

False. Combustion reactions give out energy to he surroundings

Conservation of energy is where the overall amount of energy does not change during a reaction.

False. Displacement reactions can be exothermic or endothermic depending on the substances used.

Calorimetry is a technique used to measure changes in enthalpy of chemical reactions

Specific heat capacity is the energy needed to raise the temperature of 1 g of a substance by 1 °C.

The equation for calculating heat energy change is: Q = m × c × ΔT

The main source of error in combustion calorimetry experiments is heat loss.

True. In calorimetry experiments, the specific heat capacity of the solution is assumed to be the same as pure water, i.e., 4.18 J/g/°C.

The symbol ΔT represents the temperature change.

Q represents the heat energy change.

m represents the mass of the substance being heated.

Heat loss can be reduced by using a polystyrene cup / vacuum flask or metal can as a calorimeter and placing a lid on top.

c represents the specific heat capacity.

Molar enthalpy change (ΔH) is the heat energy change per mole of substance, and it has the unit kJ per mole.

The equation for calculating molar enthalpy change is: ΔH = Q ÷ n where n is the number of moles

True. In energetics calculations, the temperature change in degrees Celsius is the same as the temperature change in Kelvin.

The units of heat energy change (Q) are Joules (J).

n represents the number of moles of the substance.

The units of molar enthalpy change (ΔH) are kilojoules per mole (kJ/mol).

True. The specific heat capacity of water is 4.18 J/g/°C.

Q represents the heat energy change for the reaction.

The heat energy change is:

Energy level diagrams are graphical representations of the relative energies of the reactants and products in chemical reactions.

An energy level diagram show that a reaction is exothermic because the energy of the products is lower than the energy of the reactants.

True. The difference in height between the energy of reactants and products on an energy level diagram represents the overall enthalpy change of a reaction.

An energy level diagram show that a reaction is endothermic because the the energy of the products is higher than the energy of the reactants.

The energy of the reactants and products is displayed on the y-axis of an energy level diagram.

The progress of the reaction is shown on the x-axis of an energy level diagram.

A downwards arrow on an energy level diagram indicates an exothermic reaction.

An upwards arrow on an energy level diagram indicates an endothermic reaction.

Bond energy is the amount of energy required to break a bond or the amount of energy given out when the bond is formed.

True. Bond breaking is an endothermic process as energy is needed to break bonds, which is absorbed from the reaction surroundings

False. When new bonds are formed, energy is released which is an exothermic reaction.

The equation used to calculate enthalpy change using bond energies is: enthalpy change (ΔH) = energy taken in - energy given out

The three steps involved in calculating the enthalpy change using bond energies are:

False. When calculating the energy required to break bonds and that released when new bonds are formed, we do need to consider the number of moles for each substance. The bond energy is multiplied by the number of moles.