Define the term exothermic reaction.
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Define the term exothermic reaction.
An exothermic reaction is a reaction that gives out heat energy to the surroundings causing the temperature of the surroundings to increase.
Define the term endothermic reaction.
An endothermic reaction is a reaction that takes in heat energy from the surroundings causing the temperature of the surroundings to decrease.
True or False?
Neutralisation reactions are exothermic reaction.
True.
Neutralisation reactions are exothermic reaction.
True or False?
Combustion reactions take in energy from the surroundings.
False.
Combustion reactions give out energy to he surroundings
What is meant by conservation of energy?
Conservation of energy is where the overall amount of energy does not change during a reaction.
True or False?
Displacement reactions are exothermic.
False.
Displacement reactions can be exothermic or endothermic depending on the substances used.
What is calorimetry?
Calorimetry is a technique used to measure changes in enthalpy of chemical reactions
Define the term specific heat capacity.
Specific heat capacity is the energy needed to raise the temperature of 1 g of a substance by 1 °C.
State the equation for calculating heat energy change, Q.
The equation for calculating heat energy change is:
Q = m × c × ΔT
What is the main source of error in combustion calorimetry experiments?
The main source of error in combustion calorimetry experiments is heat loss.
True or False?
In calorimetry experiments, the specific heat capacity of the solution is assumed to be the same as pure water.
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.
What does the symbol ΔT represent in the equation for heat energy change?
The symbol ΔT represents the temperature change.
What does the symbol Q represent in the equation for heat energy change?
Q represents the heat energy change.
What does the symbol m represent in the equation for heat energy change?
m represents the mass of the substance being heated.
How can heat loss be reduced when determining the enthalpy of a solution using calorimetry?
Heat loss can be reduced by using a polystyrene cup / vacuum flask or metal can as a calorimeter and placing a lid on top.
What does the symbol c represent in the equation for heat energy change?
c represents the specific heat capacity.
Define the term molar enthalpy change (ΔH).
Molar enthalpy change (ΔH) is the heat energy change per mole of substance, and it has the unit kJ per mole.
State the equation for calculating molar enthalpy change (ΔH)
The equation for calculating molar enthalpy change is:
ΔH = Q ÷ n
where n is the number of moles
True or False?
In energetics calculations, the temperature change in degrees Celsius is the same as the temperature change in Kelvin.
True.
In energetics calculations, the temperature change in degrees Celsius is the same as the temperature change in Kelvin.
What are the units of heat energy change, Q?
The units of heat energy change (Q) are Joules (J).
What does the symbol n represent in the equation for molar enthalpy change?
n represents the number of moles of the substance.
What are the units of molar enthalpy change (ΔH)?
The units of molar enthalpy change (ΔH) are kilojoules per mole (kJ/mol).
True or False?
The specific heat capacity of water is 4.18 J/g/°C.
True.
The specific heat capacity of water is 4.18 J/g/°C.
What does the symbol Q represent in the equation for molar enthalpy change?
Q represents the heat energy change for the reaction.
Propanol was burned and used to heat 100 g of water. The temperature rose by 20oC. Calculate the heat energy change.
The specific heat capacity of water is 4.18 J/g/°C
The heat energy change is:
Q = mcΔT
Q = 100 x 4.18 x 20
Q= 8360 J
What are energy level diagrams?
Energy level diagrams are graphical representations of the relative energies of the reactants and products in chemical reactions.
How does an energy level diagram show that a reaction is exothermic?
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 or False?
The difference in height between the energy of reactants and products on an energy level diagram represents the overall enthalpy change of a reaction.
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.
How does an energy level diagram show that a reaction is endothermic?
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.
What information is shown on the y-axis of an energy level diagram?
The energy of the reactants and products is displayed on the y-axis of an energy level diagram.
What information is shown on the x-axis of an energy level diagram?
The progress of the reaction is shown on the x-axis of an energy level diagram.
What does an downwards arrow on an energy level diagram indicate?
A downwards arrow on an energy level diagram indicates an exothermic reaction.
What does an upwards arrow on an energy level diagram indicate?
An upwards arrow on an energy level diagram indicates an endothermic reaction.
Define the term bond energy
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 or False?
Bond breaking is an endothermic process.
True.
Bond breaking is an endothermic process as energy is needed to break bonds, which is absorbed from the reaction surroundings
True or False?
Energy is taken in when bonds are formed.
False.
When new bonds are formed, energy is released which is an exothermic reaction.
State the equation used to calculate enthalpy change using bond energies.
The equation used to calculate enthalpy change using bond energies is:
enthalpy change (ΔH) = energy taken in - energy given out
Give the three steps involved in calculating the enthalpy change using bond energies.
The three steps involved in calculating the enthalpy change using bond energies are:
Calculate the energy required to break bonds
Calculate the energy released when new bonds are formed
Calculate the enthalpy change by taking the energy released away from the energy taken in
True or False?
When calculating the energy required to break bonds and the energy released when new bonds are formed, we do not need to consider the number of moles of the reactant and product.
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.