Energy Changes and Rates of Reaction Flashcards
What are physical reactions?
Reactions where a change of state takes place. They are easily reversible, no new substances are formed, and there is no change in mass
What are chemical reactions?
Atoms are rearranged. They are not easily reversible. New substances are formed, and substances involved can change mass
What is 0 degrees C in Kelvin?
273 Kelvin
What are solids like in terms of particles?
Particles are close together in a regular pattern. They do not move but vibrate. There are strong forces between particles, and they do not have much energy
What are liquids like in terms of particles?
There is some force between particles. They are close but in a random shape and can move around. They have more energy than solids but less than gases.
What are gases like in terms of particles?
There is no force between particles and they can move freely. They have lots of energy and no set shape
What are endothermic reactions?
Reactions where substances have more energy than they start with. They take in heat energy.
What are exothermic reactions?
Reactions where substances have less energy than they start with. They give out heat energy.
What are examples of endothermic reactions?
Thermal decomposition, photosynthesis, some types of electrolysis, cooking
What are examples of exothermic reactions?
Combustion, respiration, neutralisation, reactions of metals and acids
What is mexo bendo?
Making bonds is EXOthermic, Breaking bonds is ENDOthermic
Why does an exothermic reaction give out heat?
Energy is first supplied to break bonds, but then lots of energy is released when bonds are formed
Why does an endothermic reaction take in heat?
Some energy is released making bonds, but then lots is supplied breaking bonds
How is overall energy change calculated?
Overall energy change = energy required to break bonds - energy released by forming bonds
What is bond enthalpy?
The amount of energy needed to make or break a bond
What is rate of reaction?
A measure of how fast a reaction happens
What things change the rate of reaction?
Surface area, concentration or pressure, temperature
What is the formula for rate of reaction?
Rate of reaction = amount of reactant used or amount of product formed / time
How can rate of reaction be calculated?
Precipitation (disappearing cross)
Change in mass (from gas given off)
Volume of gas (using a gas syringe)
How can you work out the gradient from a curved graph?
Draw a tangent (straight line) to the point at which you need to find the gradient and measure its gradient
What needs to happen for particles to react?
They need to collide with a certain amount of energy or higher
What two factors influence rate of reaction?
Collision frequency and energy transferred
What is the minimum energy particles need to react called?
Activation energy
How can activation energy be lowered?
Using a catalyst
