Unit 4 -Energetics Flashcards
Definition of the standard molar enthalpy of formation
The standard Molar enthalpy of formation is the entropy change when one mole of substance is formed from its constituent elements under standard conditions, or reactants and products being in their standard states.
Define the standard molar enthalpy of combustion.
The standard molar enthalpy of combustion, is the enthalpy change when one mole of substance is completely burned in oxygen under standard conditions, or reactants and products being in their standard states.
Why is the amount of energy involved when a chemical reaction takes place important?
You can measure the energy values of fuels
You can calculate the energy requirements for industrial processes
You can work out the theoretical amount of energy to break bonds and the amount of energy released when bonds are made
It helps to predict whether or not an reaction will take place.
What is Thermo chemistry?
Thermal chemistry is the study of heat changes during chemical reactions.
What happens to bonds in a chemical reaction?
When a chemical reaction takes place, chemical bonds break and new ones are formed.
Energy must be put in to break bonds and energy is given out when bonds are formed, so most chemicals involve an energy change.
The overall change my results in energy being given out or taken in
What is enthalpy change?
When you measure a change at constant pressure, it is called and enthalpy change.
What are the standard conditions used for measuring enthalpy changes?
The standard conditions used for measuring it until the changes,
pressure of 100 kPa
Temperature of 298 Kelvin
When is a reaction thought to be over?
Reaction is not thought to be over until products have cooled back to 298 Kelvin
What happens in an exothermic reaction?
In an exothermic reaction the products end up with less heat energy than the starting of materials because they have lost heat energy when they heated up their surroundings. This means that delta H is negative
What happens in an endothermic reaction?
In an endothermic reaction the products end up with more energy than the starting materials, so delta H is positive, it is therefore given a positive sign
How do you measure enthalpy change for a reaction?
You need to know three things:
- ) Mass of substance being heated or called
- ) Temperature change
- ) Specific heat capacity of the substance.
What is specific heat capacity (C)?
The specific heat capacity (C) is the amount of heat needed to raise the temperature of 1 g of substance by one Kelvin.
What are the units of specific heat capacity?
Joules per gram per Kelvin
What is the equation for enthalpy change?
Q=mc🔺T
explain simple calorimetry
You can burn the fuel to heat a known mass of water and then measured the temperature rise of water. You assume that all the heat from the fuel goes into the water
