Heat Energy Changes in Chemical Reactions (Edexcel GCSE Combined Science: Chemistry): Flashcards
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- FrontHeat Energy Changes
True or False?
Temperature will increase in an exothermic reaction.
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Cards in this collection (35)
True or False?
Temperature will increase in an exothermic reaction.
True.
Temperature will increase in an exothermic reaction.
Define the term exothermic reaction.
An exothermic reaction is a reaction that transfers thermal energy to the surroundings, causing the temperature of the surroundings to increase.
True or False?
Neutralisation reactions are exothermic reactions.
True.
Neutralisation reactions are exothermic reactions.
Define the term endothermic reaction.
An endothermic reaction is a reaction that takes in thermal energy from the surroundings, causing the temperature of the surroundings to decrease.
True or False?
Combustion reactions take in energy from the surroundings.
False.
Combustion reactions give out energy to the surroundings.
Name the piece of equipment used to measure temperature changes.
The piece of equipment used to measure temperature changes is a thermometer.
True or False?
Displacement reactions are exothermic.
False.
Displacement reactions can be exothermic or endothermic depending on the substances used.
In an exothermic reaction, energy is .......... to the surroundings, causing the temperature of the surroundings to .......... .
In an exothermic reaction, energy is transferred to the surroundings, causing the temperature of the surroundings to increase.
True or False?
Precipitation reactions are endothermic.
False.
Precipitation reactions are exothermic.
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 a 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.
Explain, in terms of bond making and breaking, why a reaction is endothermic.
A reaction is endothermic because less thermal energy is transferred to the surroundings when forming bonds in the products than is required to break bonds in the reactants.
True or False?
Energy is taken in when bonds are formed.
False.
When new bonds are formed, energy is transferred to the surroundings, which is an exothermic process.
Breaking chemical bonds is an .......... process because energy must be .......... to break the bonds, whereas forming new bonds is an .......... process.
Breaking chemical bonds is an endothermic process because energy must be absorbed to break the bonds, whereas forming new bonds is an exothermic process.
True or False?
A reaction is exothermic if more heat energy is released in forming bonds in the products than is required in breaking bonds in the reactants.
True.
A reaction is exothermic if more energy is transferred to the surroundings when new bonds are formed than what was required to break them.
Give the three steps involved in calculating the energy change of a reaction using bond energies.
The three steps involved in calculating the energy change of a reaction 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
Identify the type and number of each bond being formed in the following reaction:
The type and number of each bond being formed are:
3 C-H bonds
1 C-Cl bond
1 H-Cl bond
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.
State the equation used to calculate energy change using bond energies.
The equation used to calculate energy change using bond energies is:
energy change = energy taken in − energy given out
Give the unit of energy change.
The unit of energy change is kJ mol-1.
Define bond energy.
Bond energy is the amount of energy required to break one mole of a particular covalent bond, measured in kJ mol⁻¹. The same amount of energy is released when that bond is formed.
What are reaction profiles?
Reaction profiles are graphical representations of the relative energies of the reactants and products in chemical reactions.
How does a reaction profile show that a reaction is exothermic?
A reaction profile shows 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 energy change of a reaction.
True.
The difference in height between the energy of reactants and products on an energy level diagram represents the overall energy change of a reaction.
How does a reaction profile show that a reaction is endothermic?
An energy level diagram shows that a reaction is endothermic because 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 a 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.
What does each letter represent on the reaction profile?
The letters represent:
A= reactants
B= progress of reaction
C= overall energy change
D= activation energy
What type of reaction is shown in the following reaction profile?
The following reaction profile is for an endothermic reaction.
Define the term activation energy.
Activation energy is the minimum energy colliding particles need in order to react.
True or False?
When a catalyst is added to a reaction, the energy levels of the reactants and products on the reaction profile change.
False.
A catalyst does not change the energy levels of the reactants or products. It provides an alternative reaction pathway that lowers the activation energy only.
On a reaction profile, how does adding a catalyst change the shape of the graph?
A catalyst lowers the peak (activation energy) on the reaction profile.
The reactants and products remain at the same energy levels — only the activation energy is reduced.
On a reaction profile, the .......... energy is shown by the peak of the curve, which represents the minimum energy that colliding particles need in order to react.
On a reaction profile, the activation energy is shown by the peak of the curve, which represents the minimum energy that colliding particles need in order to react.
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