The word equation for the reaction between magnesium and dilute hydrochloric acid is magnesium + hydrochloric acid → magnesium chloride + hydrogen The reaction was carried out using the apparatus shown in Figure 6 - Edexcel - GCSE Chemistry Combined Science - Question 4 - 2019 - Paper 1

Initially, the volume of hydrogen gas produced increases rapidly as magnesium reacts with hydrochloric acid. Over time, the rate of gas production slows down as the magnesium is consumed, resulting in a gradual approach to completion of the reaction.

The graph initially rises steeply, reflecting a rapid loss in mass due to the fast rate of reaction. After reaching a peak, the slope becomes less steep, indicating a slower rate of reaction as the magnesium is used up, eventually leveling off as the reaction approaches completion.