Module 4 (Drivers of Reactions) Flashcards
What is energy defined as?
Energy is defined as the capacity to do work or transfer heat
What is work defined as?
Work is defined as the energy used to cause an object with mass to move
What is the difference between the system and the surroundings?
The system refers to the reactants and products of the chemical reaction that is happening, while the surroundings refers to the actual container and everything else around it.
What are the three names which a system can be classified as?
Systems can be classified as open, closed, or isolated.
- An open system is a system which can exchange both energy and matter with its surroundings (an example of this is a stovetop).
- A closed system is a system which can only exchange energy with its surroundings, not matter (an example of this is a cup of tea with an enclosed lid).
- An isolated system is a system which cannot exchange either matter or energy with its surroundings. It is extremely rare to find an isolated system (an example of an ‘isolated’ system could be an insulated drink cooler with a lid, however, it is still not perfect, and there could be small parts which are not fully isolated).
What is the definition of heat?
Heat can be defined as the energy transferred between a system and its surroundings as a result of their difference in temperature. Heat can be measured in joules (J).
What is the difference between an endothermic and an exothermic reaction?
In an endothermic reaction, the system absorbs heat from its surroundings. An example of an endothermic reaction is the melting of ice, because energy enters the system from the surroundings (heat enters to melt the ice). In an endothermic reaction, the total chemical energy of the products is also greater than the total chemical energy of the reactants, and they also require a constant input of energy.
Other Examples of Endothermic: Boiling Water
In an exothermic reaction however, the system releases heat into the surrounding environment. An example of an exothermic reaction is combustion. In an exothermic reaction, the total chemical energy of the products is less than the total chemical energy of the reactants.
Other Examples of Exothermic: Condensation, Freezing (when water becomes a solid, it releases heat, warming up its surroundings, and the water becomes colder)
What is enthalpy?
The chemical energy of a substance is enthalpy, H. The enthalpy change heat of reaction (ΔH) refers to the exchange of heat energy between the system and the surroundings.
What is the definition of temperature?
Temperature is defined as the average kinetic energy of molecules, typically measured in Kelvin (K).
In endothermic reactions, is ΔH > 0 or is ΔH < 0?
In endothermic reactions, ΔH > 0
In exothermic reactions, is ΔH > 0 or is ΔH < 0?
In exothermic reactions, ΔH < 0
How will reversing a chemical equation change the enthalpy?
Reversing a chemical equation will simply reverse the sign of ΔH, the magnitude (actual value) of ΔH will remain the same.
What factors can influence enthalpy?
- Physical changes involve enthalpy change, so the state of the species will also affect ΔH
- Reversing a chemical reaction can also reverse the sign of ΔH, however, the magnitude of ΔH will remain the same
What is heat of combustion?
The heat of combustion is the enthalpy change that occurs when a specified amount of a substance burns completely in oxygen. Heat of combustion [ΔH (lowercase subscript c)] is measured in kJ/mol can be measured in a pure system, and this value is always negative, as combustion is an exothermic process
What formula is used to calculate the amount of energy released in heat of combustion?
energy = n x heat of combustion
where n = number of moles,
heat of combustion is ΔH with subscript c, and there’s a table of values typically provided for common substances
What does specific heat capacity refer to?
Specific heat capacity refers to the amount of heat required to raise the temperature of 1g of a substance by 1°C or 1K. It is measured in Jg^-1K^-1, but can also be expressed as Jg^-1°C^-1
