C5/8 Monitoring Reactions

What is the conservation of energy law?

Energy cannot be created or destroyed, it can only be transferred

What is an exothermic reaction?

A reaction that transfers energy to the surroundings

What is an endothermic reaction?

A reaction that takes in energy from the surroundings

What happens to the temperature of the surroundings in an exothermic reaction?

The temperature increases

What happens to the temperature of the surroundings in an endothermic reaction?

The temperature decreases

What happens to the energy of the reactants in exothermic reactions?

The reactants lose energy to form the products

What happens to the energy of the reactants in endothermic reactions?

The reactants gain energy to form the products

What are examples of exothermic reactions? (3)

combustion

many oxidation reactions

neutralisation

What type of reaction takes place in hand warmers?

exothermic

What type of reaction takes place in self heating cans

exothermic

What type of reaction are thermal decomposition reactions?

endothermic

What is a thermal decomposition reaction?

The breakdown of a substance when it is heated

What type of reaction occurs when citric acid reacts with sodium hydrogencarbonate (Baking soda)?

endothermic

What is the activation energy?

The minimum amount of energy required for a reaction to occur

What distance is labelled the activation energy on reaction profiles?

The distance from the reactants to the top of the peak

What type of reaction takes place in sports injury packs?

endothermic

What is the test for hydrogen?

Put a burning splint in the gas
If hydrogen is present it will burn with a squeaky pop

What is the test for oxygen?

Put a glowing splint in the gas
If oxygen gas is present the glowing splint will relight

What is the test for carbon dioxide?

Bubble the gas through limewater
If the gas is carbon dioxide the limewater will turn from colourless to milky

What is the test for chlorine?

Put damp litmus paper in the gas
If chlorine gas is present the litmus paper is bleached and turns white

What is a pure substance?

A substance made up of only one type of element or compound

What is an impure substance?

A substance made of more than one type of element/compound

What type of substances melt and boil at specific temperatures?

Pure substances

What type of substances melt and boil over a range of temperatures?

Impure substances

Is carbon dioxide pure or impure?

Pure

Is oxygen pure or impure?

Pure

Is water from a tap pure or impure?

Impure (it contains dissolved salts)

What is a formulation?

A mixture that has been designed as a useful product

Are formulations pure or impure?

Impure

What is chromatography used to separate?

Mixtures of soluble substances

Name the two phases in chromatography

Stationary phase - where molecules don't move around (Paper)

Mobile phase - where molecules move around (solvent)

Why do substances separate in paper chromatography? (3)

Substances move up the paper when they are dissolved in the solvent

The different substances have different solubilities

The more soluble a substance, the further it travels

How could you tell if a substance was pure or impure by looking at a chromatogram? (2)

An impure substance would have more than one dot in a vertical column above the original dot

A pure substance would only have one

Why should the baseline be drawn in pencil?

Pencil doesn’t dissolve in water but pen does.

Why should the level of water be below the baseline?

Otherwise the spots would wash off the paper

What is the solvent front?

The distance travelled by the solvent

When should you remove the chromatography paper?

When the solvent has nearly reached the top

What equation is used to calculate Rf values?

Distance travelled by spot / distance travelled by solvent