DF1: Thermochemistry Flashcards
Define “thermochemistry”
The study of energy and heat associated with chemical reactions
Define “exothermic”
A reaction that gives out energy and heats surroundings
During an exothermic reaction, are bonds formed/broken?
Formed
During an exothermic reaction, is energy released/taken in?
Released
Where does energy released from an exothermic reaction go?
Its lost to the reaction’s surroundings and heats them up
Is enthalpy change positive/negative for exothermic reactions and why?
Negative - products end up with less energy than reactants
Define “endothermic”
A reaction that takes in energy and cools the surroundings
During an endothermic reaction, are bonds formed/broken?
Broken
Is enthalpy change positive/negative for endothermic reactions and why?
Positive - products end up with more energy than reactants
Define “enthalpy change”
Amount of energy transferred to and from surroundings
Why are standard conditions used when calculating enthalpy change?
They are set conditions which allows us to compare enthalpy changes
What temperature is used in standard conditions?
298K
What pressure is used in standard conditions?
1atm
What concentration is used in standard conditions?
1moldm-3
How do you convert K to degrees C?
Minus 273
What are the 4 types of enthalpy change?
- Standard enthalpy change of a reaction
- Standard enthalpy change of formation
- Standard enthalpy change of combustion
- Standard enthalpy change of neutralisation
Define “standard enthalpy change of a reaction”
Enthalpy change when one mole of matter is transformed by a chemical reaction under standard conditions
Define “standard enthalpy change of a formation”
Enthalpy change when 1 mole of a compound is formed from its elements in their standard states, under standard conditions
Define “standard enthalpy change of a combustion”
Enthalpy change when 1 mole of a substance is completely burned in oxygen, under standard conditions
Define “standard enthalpy change of a neutralisation”
Enthalpy change when acid reacts with alkali to form 1 mole of water under standard conditions
Define “standard states”
A substance’s most stable state under standard conditions
Are all combustion reactions positive/negative and why?
Negative because they are all exothermic
What is the formula for calculating enthalpy change?
q=m x c x change in T
What is the specific heat capacity of water?
4.18Jg-1k-1
How does a bomb calorimeter work?(2)
- Fuel is ignited electrically and burns oxygen inside the pressurised vessel
- Energy is transferred to the surrounding water
What is measured in a bomb calorimeter?
Temperature rise
How is the experiment conducted in a bomb calorimeter?
At a constant volume in a closed container
Why is the fuel in a bomb calorimeter burnt under pressure?
To increase the number of successful collisions leading to complete combustion of the sample
Why is a bomb calorimeter more accurate than a simple calorimeter?
Low heat losses
