Energetics Flashcards
Brownlow
What is enthalpy change?
The change in heat content at constant pressure.
Is the change in heat in an exothermic reaction negative or positive?
Negative.
Is the change in heat in an endothermic reaction negative or positive?
Positive.
What is enthalpy?
The measure of the heat content of a substance.
What is enthalpy change?
The heat change in a reaction at a constant pressure.
What are endothermic reactions?
Reactions that absorb energy from the surroundings.
Is the enthalpy change for an endothermic reaction positive or negative?
Positive.
Why is an endothermics enthalpy change positive?
The products are higher in energy than the reactants.
What are exothermic reactions?
Reactions that release energy to the surroundings.
Why is an exothermics enthalpy change negative?
The product is lower in energy than reactants.
Is the enthalpy change for an exothermic reaction negative or positive?
Negative.
What do you need to break a bond?
Absorb energy.
Is bond breaking an endothermic or exothermic process?
Endothermic.
Why is bond breaking an endothermic process?
Energy is absorbed so the enthalpy change is positive.
If a reaction requires more energy for bonds to be broken than formed is the reaction endothermic or exothermic?
Endothermic.
What do you need to form a bond?
Release energy.
Is bond forming an exothermic or endothermic process?
An exothermic process and the enthalpy change is negative.
If a reaction releases more energy breaking bonds than it absorbs to form bonds is it endothermic or exothermic?
Exothermic.
What is the equation for enthalpy change?
Total energy to break bonds - total energy released forming bonds.
What is calorimetry?
The method used to work out the enthalpy change of combustion.
What is the first step of calorimetry for a fuel?
A fuel is burned to raise the temperature of the water by a specific amount. Generally we weigh the fuel before and after burning to work out the mass of fuel burned.
What is the second step of calorimetry for a fuel?
The energy from the fuel is transferred into the water although some is lost to the surroundings too.
Why is a lid placed on top in calorimetry for a fuel?
To prevent heat loss.
Why are wind shields placed near the flame in calorimetry for a fuel?
To prevent a draught from moving the flame.
What is the equation to calculate the energy transferred in calorimetry?
q = M * c * delta T
What does q stand for in the equation to calculate the energy transferred in calorimetry?
Heat energy lost or gained.
What does m stand for in the equation to calculate the energy transferred in calorimetry?
MAss of water or solution.
What does c stand for in the equation to calculate the energy transferred in calorimetry?
Specific heat capacity of water.
What does delta T stand for in the equation to calculate the energy transferred in calorimetry?
Temperature change.
What unit is temperature measured in the equation used to calculate the energy transferred in calorimetry?
Kelvin.
What unit is mass measured in the equation used to calculate the energy transferred in calorimetry?
Grams.
What unit is heat or energy lost or gained measured in the equation used to calculate the energy transferred in calorimetry?
Joules.
What is the specific heat capacity of water?
4.18 Jg^-1K^-1.
What is the first step of calorimetry of a solution?
Add acid and mesure temperature.
What is the second step of calorimetry of a solution?
Add alklai/solid and stir and measure temperature change.
What does Hess’ law state?
The total enthalpy change of a reaction is independent of the route taken.
