What is an endothermic reaction?

One that takes in energy from the surroundings, so the temperature falls.

Give two examples of exothermic reactions.

Combustion and neutralisation (also rusting of iron).

Give two examples of endothermic processes.

Thermal decomposition and photosynthesis.

How does a hand warmer work?

An exothermic reaction (iron reacting with oxygen) releases heat.

Why does an instant cold pack feel cold?

An endothermic change takes in energy from the surroundings, including your skin.

The temperature change: final temperature minus starting temperature.

How do you calculate the energy released per gram of fuel?

Energy transferred to the water (Q) divided by the mass of fuel burned.

How do you calculate the energy released per mole of fuel?

Divide Q by the moles of fuel burned, where moles = mass ÷ Mr.

Why is the energy found by calorimetry lower than the data book value?

Heat is lost to the surroundings and the can, and combustion may be incomplete.

Name one way to reduce heat loss in a fuel experiment.

Use a draught shield, insulate the can or put a lid on it.

Exothermic and endothermic reactions and calorimetryIB MYP Chemistry: Flashcards

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What is an exothermic reaction?

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What is an exothermic reaction?: One that releases energy to the surroundings, so the temperature rises.
What is an endothermic reaction?: One that takes in energy from the surroundings, so the temperature falls.
Give two examples of exothermic reactions.: Combustion and neutralisation (also rusting of iron).
Give two examples of endothermic processes.: Thermal decomposition and photosynthesis.
How does a hand warmer work?: An exothermic reaction (iron reacting with oxygen) releases heat.
Why does an instant cold pack feel cold?: An endothermic change takes in energy from the surroundings, including your skin.
Write the calorimetry equation.: Q = m × c × ΔT
What is the specific heat capacity of water?: 4.18 J/g/°C
What is ΔT?: The temperature change: final temperature minus starting temperature.
How do you change joules into kilojoules?: Divide by 1000.
How do you calculate the energy released per gram of fuel?: Energy transferred to the water (Q) divided by the mass of fuel burned.
How do you calculate the energy released per mole of fuel?: Divide Q by the moles of fuel burned, where moles = mass ÷ Mr.
Why is the energy found by calorimetry lower than the data book value?: Heat is lost to the surroundings and the can, and combustion may be incomplete.
Name one way to reduce heat loss in a fuel experiment.: Use a draught shield, insulate the can or put a lid on it.

Exam questions on Exothermic and endothermic reactions and calorimetry

A hiker in Chile carries a disposable hand warmer. When she opens the sachet, the iron powder inside reacts with oxygen from the air and the sachet warms to about 55 °C for several hours. Her friend carries an instant cold pack for sports injuries. When the pack is squeezed, a solid dissolves in water inside it and the pack quickly becomes cold.
Explain, in terms of energy transfer, why the hand warmer feels warm but the cold pack feels cold.2 marks
A student in Kuala Lumpur burns ethanol in a spirit burner to heat 100 g of water in a metal can. The temperature of the water rises from 20.0 °C to 52.0 °C. The mass of the spirit burner falls from 85.40 g to 84.65 g. The specific heat capacity of water is 4.18 J/g/°C.
Calculate the energy transferred to the water, in joules.2 marks
Students at a school in Lagos compare two liquid fuels, ethanol and propan-1-ol, to find which releases more energy per gram. They burn each fuel in a spirit burner to heat 100 g of water in a metal can. Burning 0.80 g of ethanol raises the temperature of the water by 30.0 °C. Burning 0.70 g of propan-1-ol raises the temperature of the water by 33.0 °C. The specific heat capacity of water is 4.18 J/g/°C. The data book value for propan-1-ol is 33.6 kJ/g.
State two variables that the students should control to make the comparison fair, and one safety precaution they should take.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).