A student planned an experiment to find out which substance would produce the biggest temperature decrease when added to either water or an acid. The chemicals she had access to were: ammonium nitrate solid sodium hydroxide solution citric acid solution sodium hydrogen carbonate solution water dilute hydrochloric acid State one problem the student would have in making this fair test.

Dissolution of solid ammonium nitrate in water and the reaction between Sodium hydrogen carbonate reacts with citric acid are endothermic reaction. This can be decided by touching the test-tube of the reaction mixture. To determine the biggest temperature decrease, a suitable apparatus is not provided.

A student planned an experiment to find out which substance would produce the biggest temperature decrease when added to either water or an acid. The chemicals she had access to were: ammonium nitrate solid sodium hydroxide solution citric acid solution sodium hydrogen carbonate solution water dilute hydrochloric acid How would you improve this method.

To determine the biggest temperature decrease, a suitable apparatus, laboratory thermometer must be used. Dissolution of solid ammonium nitrate in water shows the temperature difference of 19 ° C and the reaction between Sodium hydrogen carbonate reacts with citric acid shows the temperature difference of 5 ° C . Hence, dissolution of solid ammonium nitrate in water has the biggest temperature decrease.

Jonathan carried out an experiment to measure the temperature change when two solutions are mixed. His results are shown below. Reaction Temperature at start ° C Temperature at end ° C Sodium hydrogen carbonate solution + Citric acid 21 18 Sodium hydroxide solution + Citric acid 21 23 Dilute hydrochloric acid + Citric acid solution 21 21 What were the dependent and independent variables in this experiment?

The independent variables is called independent because it is independent of the outcome being measured. This factor is deliberately manipulated in an experiment. For example, temperature. The dependent variable is influenced by the independent variable. For experiment, volume and mass.

Jonathan carried out an experiment to measure the temperature change when two solutions are mixed. His results are shown below. Reaction Temperature, t 1 ° C at start Temperature, t 2 ° C at end Sodium hydrogen carbonate solution + Citric acid 21 18 Sodium hydroxide solution + Citric acid 21 23 Dilute hydrochloric acid + Citric acid solution 21 21 State one variable that Jonathan should have controlled in this experiment.

A controlled experimental variable is a quantity that does not change in value during an experiment. These may affect the outcome and make it an unfair test. In this experiment, Jonathan should have controlled stirring of the mixture.

Jonathan carried out an experiment to measure the temperature change when two solutions are mixed. His results are shown below. Reaction Temperature t 1 , at start ° C Temperature t 2 , at end ° C Sodium hydrogen carbonate solution + Citric acid 21 18 Sodium hydroxide solution + Citric acid 21 23 Dilute hydrochloric acid + Citric acid solution 21 21 Which one of these reactions would be the most suitable for use in making an instant cold pack? Explain your answer.

To make an instant cold pack, the reaction must be endothermic. In such reaction, heat energy is absorbed from the surroundings. Hence, the most suitable mixture for use in making an instant cold pack is a mixture of Sodium hydrogen carbonate and Citric acid. In this mixture t 2 < t 1 . Hence, it is endothermic.

Jonathan carried out an experiment to measure the temperature change when two solutions are mixed. His results are shown below. Reaction Temperature t 1 , at start ° C Temperature t 2 , at end ° C Sodium hydrogen carbonate solution + Citric acid 21 18 Sodium hydroxide solution + Citric acid 21 23 Dilute hydrochloric acid + Citric acid solution 21 21 What type of the reaction is second reaction?

In the reaction between Sodium hydroxide and Citrus acid, t 2 > t 1 , i.e., the final temperature is slightly greater than initial temperature. Hence, it is an exothermic reaction. In such reaction, heat energy is liberated to the surroundings.

The diagram shows the particles in a liquid that is evaporating. How can you tell from the diagram that the liquid is evaporating?

Evaporation is conversion of liquid to gaseous form below its boiling point. It is an endothermic process. In the diagram, we can see the few molecules of liquids are oriented upwards. The molecules are far away from each which implies in gaseous state.

The diagram shows the particles in a liquid that is evaporating. Explain why evaporation causes the temperature of the liquid to decrease?

Evaporation is conversion of liquid to gaseous form below its boiling point. It is an endothermic process. As the temperature increases, the kinetic energy of molecules also increases. It is proportional to temperature. As the faster-moving molecules escape, the remaining molecules have lower average kinetic energy, and the temperature of the liquid decreases.

MEDIUM

Lower Secondary Stage 9

IMPORTANT

Earn 100

Instant cold packs can be made using ammonium nitrate and water. The pack contains a small bag of solid ammonium nitrate. This bag is inside another bag, which is full of water. When you squeeze the outer bag the smaller bag bursts. The ammonium nitrate dissolves in water and the pack becomes cold.

Explain how you know this.

Important Questions on Energy Transfers in Chemistry

MEDIUM

Lower Secondary Stage 9

IMPORTANT

Cambridge Lower Secondary Science Stage 9: Student's Book>Chapter 8 - Energy Transfers in Chemistry>End of Chapter Review>Q 10

A student planned an experiment to find out which substance would produce the biggest temperature decrease when added to either water or an acid. The chemicals she had access to were:

ammonium nitrate solid
sodium hydroxide solution
citric acid solution
sodium hydrogen carbonate solution
water
dilute hydrochloric acid

State one problem the student would have in making this fair test.

MEDIUM

Lower Secondary Stage 9

IMPORTANT

Cambridge Lower Secondary Science Stage 9: Student's Book>Chapter 8 - Energy Transfers in Chemistry>End of Chapter Review>Q 10

A student planned an experiment to find out which substance would produce the biggest temperature decrease when added to either water or an acid. The chemicals she had access to were:

ammonium nitrate solid
sodium hydroxide solution
citric acid solution
sodium hydrogen carbonate solution
water
dilute hydrochloric acid

How would you improve this method.

MEDIUM

Lower Secondary Stage 9

IMPORTANT

Cambridge Lower Secondary Science Stage 9: Student's Book>Chapter 8 - Energy Transfers in Chemistry>End of Chapter Review>Q 11

Jonathan carried out an experiment to measure the temperature change when two solutions are mixed. His results are shown below.

Reaction	Temperature at start $(° C)$	Temperature at end $(° C)$
Sodium hydrogen carbonate solution + Citric acid	$21$	$18$
Sodium hydroxide solution + Citric acid	$21$	$23$
Dilute hydrochloric acid + Citric acid solution	$21$	$21$

What were the dependent and independent variables in this experiment?

MEDIUM

Lower Secondary Stage 9

IMPORTANT

Cambridge Lower Secondary Science Stage 9: Student's Book>Chapter 8 - Energy Transfers in Chemistry>End of Chapter Review>Q 11

Jonathan carried out an experiment to measure the temperature change when two solutions are mixed. His results are shown below.

Reaction	Temperature, $t_{1} ° C$ at start	Temperature, $t_{2} ° C$ at end
Sodium hydrogen carbonate solution + Citric acid	$21$	$18$
Sodium hydroxide solution + Citric acid	$21$	$23$
Dilute hydrochloric acid + Citric acid solution	$21$	$21$

State one variable that Jonathan should have controlled in this experiment.

MEDIUM

Lower Secondary Stage 9

IMPORTANT

Cambridge Lower Secondary Science Stage 9: Student's Book>Chapter 8 - Energy Transfers in Chemistry>End of Chapter Review>Q 11

Jonathan carried out an experiment to measure the temperature change when two solutions are mixed. His results are shown below.

Reaction	Temperature $t_{1}$ , at start $(° C)$	Temperature $t_{2}$ , at end $(° C)$
Sodium hydrogen carbonate solution + Citric acid	$21$	$18$
Sodium hydroxide solution + Citric acid	$21$	$23$
Dilute hydrochloric acid + Citric acid solution	$21$	$21$

Which one of these reactions would be the most suitable for use in making an instant cold pack? Explain your answer.

EASY

Lower Secondary Stage 9

IMPORTANT

Cambridge Lower Secondary Science Stage 9: Student's Book>Chapter 8 - Energy Transfers in Chemistry>End of Chapter Review>Q 11

Jonathan carried out an experiment to measure the temperature change when two solutions are mixed. His results are shown below.

Reaction	Temperature $t_{1}$ , at start $(° C)$	Temperature $t_{2}$ , at end $(° C)$
Sodium hydrogen carbonate solution + Citric acid	$21$	$18$
Sodium hydroxide solution + Citric acid	$21$	$23$
Dilute hydrochloric acid + Citric acid solution	$21$	$21$