Energy Changes

Question 1

What is conservation of energy?

Answer 1

-The total amount of energy in the universe at the end of a reaction is the same as it was before
-When a reaction happens energy is transferred too or from the surroundings
-Exothermic- Combustion, oxidation, neutralisation, self-heating cans and hand warmers
-Endothermic- Thermal decomposition, the reaction of citric acid and sodium hydrogen carbonate, instant icepacks

Question 2

What is the method to react two solutions?

Answer 2

-Place the polystyrene cup inside the glass beaker to make it more stable
-Measure an appropriate volume of each liquid, eg 25cm^3
-Place on of the liquids in a polystyrene cup
-Record the temperature of the solution
-Add the second solution and record the highest or lowest temperature obtained
-Change your independent variable and repeat the experiment, your independent variable could be the concentration of one of the reactants, or the type of acid/alkali being used, or the type of metal/metal carbonate being used

Question 3

What is the methods for reacting a solid with a solution?

Answer 3

-Place the polystyrene cup inside the glass beaker to make it more stable
-Measure an appropriate volume of the solution, eg 25cm^3
-Measure an appropriate mass of t he solid, or select a suitable sized piece of metal
-Place the solution in a polystyrene cup
-Record the temperature of the solution
-Add the solid and record the highest or lowest temperature obtained
-Change your independent variable and repeat the experiment. The independent variable could be the surface area of the solid, or the type of acid being used, or the type of metal being used

Question 4

What are the reaction profiles?

Answer 4

-Exothermic- Energy level decreases
-Endothermic- Energy level increases
-Activation Energy- The minimum energy needed by particles when they collide for a reaction to occur
-Activation energy line goes from the reactants to the ‘hump’/top

Question 5

What are breaking and forming bonds?

Answer 5

-Breaking- Endothermic- Energy is taken in
-Forming- Exothermic- Energy is given out
-In a reaction, bonds are broken and then new bonds are made
-Exothermic if more heat energy is released in making bonds than is taken in when breaking bonds
-Endothermic if less heat energy is released in making bonds than is breaking bonds