Physical Chemistry Flashcards
Define an Exothermic Reaction:
- Gives out energy to surroundings in form of heat
- Shown by rise in temperature of surroundings
- Negative enthalpy change
Define Endothermic Reaction:
- Takes in energy from surroundings in form of heat
- Shown by fall in temperature of surroundings
- Positive enthalpy change
What is Enthalpy Change?
The overall change in energy in reaction
What is the Reaction Profile of an Exothermic Reaction?
- Products lower energy than reactants
* Difference In height = energy given out in reaction
What is the Activation Energy?
- Minimum amount of energy the reactants need to collide with each other and react
- Initial rise in energy - energy needed to start reaction
- Amount of energy particles need to break bonds
What is the Reaction Profile for an Endothermic Reaction?
- Products higher energy than reactants
* Difference In height = energy taken in in reaction
What is Calorimetry?
- Use to find Enthalpy Change
* Measure amount of energy transferred in chemical reaction
How do you measure Energy Transferred in Dissolving, Displacement and Neutralisation Reactions?
- Get temperature of reactions (same temp)
- Mix then
- Measure temperature of solution at end
How can you measure the Energy Transferred in Neutralisation Reaction between Hydrochloric Acid (HCl) and Sodium Hydroxide (NaOH)?
- 25cm^3 HCl and NaOH in separate beakers
- Beakers In water bath at 25 degrees
- Add HCl, then NaOH to polystyrene cup
- Take temperature of mixture every 30secs, record highest temperature
How do you do an Combustion Experiment to Calculate Enthalpy Change?
- 50g water in copper can & record temperature
- Weigh spirit burner & lid
- Flame to heat water, stir until 50 degrees
- Method uses metal container (made of copper - conducts heat)
- Put our flame
- Weigh spirit burner & lid
- Calculate enthalpy change
Heat Energy Transferred =
Mass if liquid being heated x 4.2 x change in temperature of liquid
What happens during chemical reactions?
•Old bones are broken and new bonds are formed
Why is bond formation an exothermic process?
Energy is released when you bonds are formed
Why is bond formation an endothermic process?
Energy must be supplied to break existing bonds
Enthalpy change =
Total energy absorbed to break bonds - Total energy released in making bonds
What is a Rate of a Chemical Reaction?
How fast the reactants are changed in products
Steeper line =
Faster rate of reaction
What does the Rate of a Chemical Reaction depend on?
•Collision frequency of particles -more collisions = faster reaction •Energy transferred during collision- particles collide with enough energy to be successful
What Factors affect the Rate of Reaction?
- Temperature
- Surface area
- Catalyst
- Concentration of solution/pressure of gas
What happens if you double Concentration/Pressure/Surface Area to Rate?
- Double number of particles available
- Frequency of collisions increase
- Rate increases
What happens if you Increase Temperature or have a Catalyst to Rate?
- Increase number of particles with enough energy
- Increase proportion of collisions which are successful
- Rate increases
What is a Catalyst?
Substance which increases rate of reaction, without being chemically changed or used up in the reaction
How can you see the Effect of Catalyst using a Reaction Profile?
Highest point on curve for reaction with a catalyst than without a catalyst
Rate of Reaction =
Amount of reactant used or amount of product formed / time
