chemistry: endothermic and exothermic paper 1

What are exothermic reactions?

They transfer energy from reacting molecules to the surroundings.

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

Temperature of surroundings increases

Is combustion endothermic or exothermic?

Exothermic

Is neutralisation an endothermic or exothermic reaction?

Exothermic reaction.

What type of reaction are certain oxidisations?

Exothermic.

In exothermic reactions, do the products have less energy than the reactants or more energy than the reactants? Why?

Less energy.

Energy is being transferred from the reaction to the surroundings.

What does the difference between the energy of the reactants and the energy of the products tell us?

Tells us the energy that has been released to the surroundings

What can exothermic reactions be used for?

Hand warmers, self heating cans for food or drink.

What are endothermic reactions?

Reactions that take in energy from their surroundings.

What happens to the temperature of the surroundings in endothermic reactions?

The temperature decreases, it gets colder.

Is thermal decomposition a exothermic or endothermic reactions?

Endothermic.

Do the products have more energy or less energy than the reactants in an endothermic reaction? Why?

The products have more energy than the reactants.

Energy is being taken in from the surroundings.

How can reactions occur?

When the particles collide with each other. They must have sufficient energy.

What is the activation energy?

The minimum amount of energy that particles have in order to react.

Where is the activation energy point on an energy profile diagram?

From the reactants to the peak of the curve.

When we break a chemical bond this requires _______ energy.

Endothermic

Making bonds released _______ energy

Exothermic

What is the independent variable of the sodium hydroxide and hydrochloric acid neutralisation temperature change reaction?

The volume of sodium hydroxide solution

What is the dependent variable of the sodium hydroxide and hydrochloric acid neutralisation temperature change reaction?

The maximum temperature reached.

What is the control variables of the sodium hydroxide and hydrochloric acid neutralisation temperature change reaction?

The volume of hydrochloric acid

The concentration of both the acid and solution.

How do you carry out the sodium hydroxide and hydrochloric acid neutralisation temperature change required practical?

1. Measure 30cm³ dilute hydrochloric acid in measuring cylinder.

2. Transfer to polystyrene cup and place that in a beaker →wont fall.

3. Measure temp of acid with thermometer, record in table.

4. Measure 5cm³ sodium hydroxide and pour into same cup.

5. Place lid on cup and place bulb thermometer through hole on cup.

6. Stir thermometer, record highest temp reach.

7. Rinse cup and repeat experiment with 10cm³ sodium hydroxide and carry out more times, increasing it by 5cm³ until at 40cm³ (twice).

8. Calculate mean value of maximum temperature needed.

What happens to the temperature as you increase the volume of sodium hydroxide solution? Why? When does it change?

Maximum temperature increases.

When adding more particles of sodium hydroxide, they react with hydrochloric acid, more energy released so temp increases.

Soon the temperature maximum begins to decreases as there is too much sodium hydroxide. This means some are unable to react.

What is concluded when there is too much sodium hydroxide? (Think energy)

Some of the hydrochloric acid isn't able to react. The energy released by the reaction has reached it's maximum.

Why does the maximum temperature actually decrease from this point? In neutralisation temperature change reaction.

Greater volume of solution is added to acid. Energy released is now spread out into a greater volume. So the maximum temperature decreases.

Why is a polystyrene cup with a lid used in the neutralisation temperature change reaction?

We are measuring temperature. We want to reduce any heat losses

Polystyrene is a good thermal insulator→ reduce heat loss through sides/bottom.

Lid→ heat loss to the air.